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A dry suit or drysuit provides thermal insulation or passive thermal protection to the wearer while immersed in water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold water. A dry suit normally protects the whole body except the head, hands, and possibly the feet. In some configurations, however, all of these are covered as well. Dry suits are used typically in these cases:
- where the water temperature is below 15°C (60°F).
- for extended immersion in water above 15°C (60°F), where discomfort would be experienced by a wet suit user.
- with an integral helmet, boots, and gloves for personal protection when working in and around hazardous liquids.
The main difference between dry suits and wetsuits is that dry suits are designed to prevent water entering. This generally allows better insulation making them more suitable for use in cold water. Dry suits can be uncomfortably hot in warm or hot air, and are typically more expensive and more complex to don. For divers, they add some degree of complexity as the suit must be inflated and deflated with changes in depth in order to avoid "squeeze" on descent or uncontrolled rapid ascent due to over-buoyancy.
Parts of a dry suit 
Membrane dry suits are made from thin materials, and thus by themselves have little thermal insulation. They are commonly made of vulcanized rubber, or laminated layers of nylon and butyl rubber. Membrane dry suits typically do not stretch, so they need to be made oversized and baggy to allow flexibility at the joints through the wearer's range of motion. This makes membrane dry suits easy to put on and get off, provides a great range of motion for the wearer, and makes them comfortable to wear for long periods, as the wearer does not have to pull against rubber elasticity.
To stay warm in a membrane suit, the wearer must wear an insulating undersuit, today typically made with polyester or other synthetic fiber batting. Polyester and other synthetics are preferred over natural materials, since synthetic materials have better insulating properties when damp or wet from sweat, seepage, or a leak. (Except for wool, which is an effective insulator when damp, albeit bulky.)
Reasonable care must be taken not to puncture or tear membrane dry suits, because buoyancy and insulation depend completely on the gas pockets in the undersuit (whereas a wetsuit normally allows water to enter, and retains its insulation despite it). The dry suit material offers essentially no buoyancy or insulation itself, so if the dry suit leaks or is torn, water can soak the undersuit, with a corresponding loss of buoyancy and insulation.
In warmer waters, some wearers wear specially designed membrane dry suits without an undersuit. These are different in design, materials, and construction from dry suits made for cold water diving.
Membrane dry suits may also be made of a waterproof and breathable material to enable comfortable wear when out of the water for long periods of time. Sailors and boaters who intend to stay out of the water prefer this type of suit.
Neoprene is a type of synthetic rubber. Neoprene can be foamed during manufacture to contain millions of tiny enclosed gas bubbles, forming a buoyant and thermally-insulating material, called "foamed neoprene", "foam-neoprene" or "expanded neoprene". Foamed neoprene may used as the fabric of a drysuit, providing some insulation due to the gas within the material, as in a standard wetsuit. If torn or punctured, leading to flooding, a foam-neoprene suit retains the insulation and buoyancy of the gas bubbles, in the same manner as in a foamed-neoprene wet suit.
Neoprene dry suits are not as easy to put on and remove as are membrane dry suits, largely due to a closer fit which is possible due to the inherent elasticity of the material, and partly due to greater weight. As with wet suits, their buoyancy and thermal protection decreases with depth as the air bubbles in the neoprene are compressed. The air or other gas in the dry fabric undergarments providing insulation under a dry suit is also compressd, but can be restored to an effective volume by inflating the drysuit at depth through an inflator valve, thus preventing "suit squeeze" and compacting of the air-filled dry fabric beneath.
Foam-neoprene also tends to shrink over the years as it outgases and slowly becomes less flexible as it ages. An alternative is crushed or compressed foam neoprene, which is less susceptible to volume changes when under pressure, and shrinks less, while retaining the elasticity which allows freedom of movement.
Foamed-neoprene dry suits provide some insulation by themselves, but even with foam drysuits, thermal under-suits are usually worn. With a thicker foamed neoprene suit, less insulation is needed underneath. The undersuits vary from a standard wet suit (worn dry), to polyester fabrics used in mountaineering and other cold weather uses (these may also be in pieces, including vests and sleeveless vests). Such fabrics also ultimately insulate in the same way as foam, using air in which convection is retarded by the small sizes of the air spaces. However, per volume and weight of fabric, the best-insulating dry polyester fabrics are more effective than foam, because their air pockets are smaller.
The combination of neoprene suit and polyester undergarment often reduces the amount of ballast needed to counteract the total buoyancy of the diver, since the total amount of air is usually less than needed for the same insulation in a membrane suit with a thicker undersuit. Notwithstanding the greater insulating power of dry fabrics, membrane suits with undersuits are a combination which usually uses the total volume of insulating air less efficiently[clarification needed] (hence uses more air for the same insulation). This is because such suits cause larger volumes of air to be present as large bubbles and spaces, and the phenomena of convection and poor distribution causes such air to be "wasted" in its value as insulator.
Hybrid suits combine the features of both types, with a membrane top attached to a neoprene bottom near the waist. The neoprene part is usually configured as a sleeveless "farmer-john" that covers the torso as well. This style is often used for surface water sports, especially in very cold water. The tight fitting lower part lets the wearer kick while swimming, and the loose fitting top allows easy arm movement. The torso covering also provides additional self-rescue or survival time if the suit leaks.
Seals at the wrists and neck prevent water entering the suit by a close contact fit against the skin around the wrists and neck. The seals are not absolutely watertight, however, and the wearer may experience some seepage during use. The wearer will also get damp due to sweat and condensation. The seals are typically made from latex rubber or foam neoprene, but are also available in silicone rubber. Latex seals are supple but easily damaged and deteriorate with exposure to oils, oxygen, and other materials, so they must be replaced periodically, every two years or more. Latex also causes an allergic reaction in some users. Neoprene seals last longer and are non-allergenic, but, being less elastic, let more water enter because they do not seal as effectively as latex seals to the contours of wrist and neck. They are also typically glued and sewn together to form a ring, and may leak along that seam.
A recent innovation is the silicone seal, which is claimed to be as supple as latex, more flexible, yet far more durable. These have not yet been widely adopted but represent a promising development.
Waterproof entry 
Modern dry suits have a waterproof zipper for entry and exit which was originally developed by NASA to hold air inside astronaut space suits. This complex and special zipper is one of the most expensive parts of the suit. The zipper is commonly installed across the back of the shoulders, since this placement compromises overall flexibility the least—but this design normally means the wearer requires assistance in donning and doffing the suit. The other most common zipper placement in modern suits is diagonally across the torso, which allows self-donning. Other designs place the zipper on the side, straight down the middle of the front or back, or on a wide tubular chest entry opening which is folded down and clipped round the waist after sealing the zip.
There are many zipper arrangements in use, because the waterproof-zipper is very rigid, and cannot stretch at all, which can make it difficult for a user to get into and out of the suit. The zipper opening is often quite small, since a large zipper makes the suit stiffer and more difficult to use. Some complex zipper arrangements that wrap around the neck or chest let the suit swing open with a flap or hinge point. Some snug-fitting suits may also use wrap-around expansion zippers that allow the suit to expand or contract to fit different size people.[clarification needed]
Dry suits may also be fitted with an extra waterproof zipper "fly" to let the user urinate when out of the water when the suit is worn for long periods.
Before true-waterproof zippers were invented, other methods of keeping the suit waterproof at the entry point had to be devised, with the most common being a long rubber entry tunnel which would be flattened shut, then rolled together from the sides and finally folded and clamped with a metal clip. An early example was the Sladen suit, where the entry tunnel was at the navel. The Louisiana-based dry suit company Aquala still makes a "historical" diving suit of that kind.
Another type of entry featured a rubber tunnel that protruded through a normal cloth zipper. The tunnel would be rolled shut and the zipper closed to hold the roll in place.
Some types did not use a zipper at all. At least one make of old-type British frogman's dry suit was one-piece with a wide neck hole for entry; the bottom of the hood and the edge of the suit's neck hole were held together by a large circular steel clamp around the neck; there was a watertight seal in the bottom of the hood. Two-piece dry suit designs in full length for year-round use and "shorty" styles for summer-season use were also common in the 1950s and early 1960s. Two-piece suits of the period include the American-made Spearfisherman frogman suit, U.S. Divers Seal Suit and the So Lo Marx Skooba Totes suit, the Italian-made Pirelli suit and the UK-made Heinke Delta suit and Siebe-Heinke Dip suit. These suits were sealed at the waist by rolling together the excess material at the bottom of the shirt and the top of the pants. A cummerbund, rail, or surgical tubing was sometimes provided to make the seal more waterproof. A modern version of the two-piece dry suit is manufactured by Customworks of Idaho. Though lacking such features as valves and zippers, these suits still have certain advantages over their modern counterparts. For example, they are cheaper, less bulky, more easily repaired and the footed pants could also double as fishing waders.
Thermal undersuits 
For cold-water use, especially diving under ice sheets, the user will usually wear a thick undersuit in a membrane dry suit. The thickness of undersuits varies and can be chosen by the wearer according the water temperature. Thinsulate is one of the preferred fabrics for undersuits. More recently, aerogel material is being added to conventional undergarments to increase the insulating properties of those garments. Neoprene dry suits are made from a foam-rubber sheet containing tiny air bubbles, which provide insulation by themselves, and can eliminate the need for an undersuit, or greatly reduce the thickness needed for the underfabric. A neoprene wet suit can also be worn under a membrane dry suit for extra protection against condensation and leaks.
Gloves, mitts, and 3-finger mitts 
Dry suits may have wrist seals, permanently attached gloves/mitts, or a third option known as the attachment ring (described below).
If it is not important to have exposed bare hands, permanently attached heavy rubber gloves or mitts can help make getting in and out of the suit much easier since there is no need for the suit to tightly seal around the wrists. Instead, the wearer can slip into the attached gloves as if they were a loose-fitting coat sleeve.
Full-hand diving mitts can be sometimes useful in extreme environments such as ice diving.
Three-finger mitts are a midpoint between gloves and mittens. In the three-finger mitts, the fingers are arranged with the index finger in a separate pocket to the other three fingers. This provides slightly better hand-grasping dexterity while still permitting heavy insulation around the hands.
The dry suit may also have an integrated hood, which seals water out around the wearer's face, and helps keep the wearer's head warm. The integrated hood is often latex rubber that fits tightly around the head, but can also be made from neoprene or membrane to allow an insulating cap to be worn under the hood. Care must be taken to avoid the hood making a waterproof seal around either of the ears, as this would risk an eardrum bursting outwards at depth.
Separate (non integral) hoods are of two types: one which extends only to the base of the neck, and the other a standard wetsuit hood with a large flange. Hoods are never tucked into the neck seal as they would be tucked into a wetsuit, as this would compromise the watertight integrity of the seal. Some suits are designed with a second (non-watertight) collar around the neck seal, which allows the flange of a standard wetsuit hood to tuck in around the outside of the seal. This can keep the neck significantly warmer, since the seal itself provides little insulation.
When a diver needs to be underwater for long periods of time day after day, a snug-fitting elastic hood can cause uncomfortable pressure sores on the ears, face, and jaw. To alleviate this and to permit easy communication with the surface and between divers, a hard metal or plastic diving helmet may be worn with the dry suit. This can be separate from the dry suit with its own watertight neck seal, or it can be permanently attached with a neck ring, and air from the helmet can enter into the suit. This can result in injury or death if not worn properly.[clarification needed]
Most commercial diving dry suits have heavy built-in boots. Sport diving suits may have boots or thin sheet-rubber booties. Surface dry suits may have booties or ankle seals to allow better foot control of water skis and surfboards. Surface dry suits may be used with separate non-waterproof neoprene booties for foot warmth, and aqua-shoes for protection while using personal watercraft.
For a commercial environment where the option of interchangeable boots for different sizes of feet is desired, the legs of the dry suit can also be fitted with attachment rings (described below). Some commercial divers order their suits without boots and install rubber work boots such as those used by miners or firefighters.
Weight boots 
For commercial dry suit divers who must work on the sea bottom or on an underwater platform (such as under an oil platform), the dry suit may be fitted with heavy metal boots to keep the diver firmly weighted down. This allows the suit to be comfortably inflated like a balloon as the diver works, without concern that the diver may float uncontrollably to the surface. These divers cannot swim freely, and may need to ride an underwater cable elevator down to the work area.
Attachment rings 
These are typically only seen on professional and commercial diving suits. They allow separate neck seals, gloves, and boots to be joined to the suit with a watertight seal. The attachment ring system uses a support ring inside the suit and a clamping band outside the suit to tightly hold the suit and the separate hood/boot/glove together. They were also used with the neck seals of some old British frogman-type dry suits (see above).
The support ring can optionally be slipped into the sleeve of a regular dry suit that has wrist seals, to temporarily put watertight rubber gloves on the suit, or the wrist seals can be removed and the inner support ring is permanently attached inside the sleeve. The support ring may be a large one-piece unit that can be slipped over the head/hands/feet, or it may be split into halves that can be directly installed up close around the neck/wrists/ankles.
Attachment rings let a commercial diver change his suit to best perform the task at hand. Wrist seals can still be used with an attachment ring suit; they are mounted onto the ring like a pair of gloves.
A typical diving dry suit has an air exhaust valve, which lets the diver vent gas from the suit during the ascent. This is necessary because when the diver ascends, the air in the suit expands, balloons out the suit, and hinders movement. The air in a ballooned suit can overcome the diver's neutral buoyancy, and can cause a sudden uncontrolled ascent to the surface, resulting in decompression sickness from missed decompression stops, or arterial gas embolism from over-expansion of the lungs.
Exhaust valves can be automatic, operating as pressure relief valves, or manual, where the diver must actuate the valve to vent. Most modern suits have an adjustable exhaust on the shoulder which can be set to release at varying pressures, closed completely, (manual operation only) or operated manually at any setting. In most situations, the diver can leave the valve "open" throughout the dive so that it releases with a moderate amount of pressure, and needs only to raise his arm while in a vertical position in order to vent the suit. With this technique, the suit will vent as needed automatically as the diver ascends. Automatic vents are generally at the shoulder, and manual vents are at the wrist. Some older dry suits have no vents, but the diver must lift one of the wrist seals or the neck seal open to vent the dry suit. Surface dry suits do not normally have exhaust valves, but the wearer may vent excess air by crouching down, "hugging" his legs, and slipping a finger under the neck seal.
Because the air inside the suit is compressed as the diver descends, a modern diving dry suit also has a gas inflation valve, which lets the diver control the buoyancy of the suit by injecting gas from a diving cylinder to avoid the suit from being squeezed tightly and painfully onto the diver's body during descent. The sensation is similar to being pinched, but all over the body. Suit squeeze can also hinder the diver's movement and make swimming more difficult. Suit squeeze also compresses insulating garments and thus reduces thermal protection.
Some old-type frogman's dry suits had a small "jack cylinder" from which they could be inflated. Otherwise the frogman (who was using an oxygen rebreather, and so limited to about 30 feet (9.144 m) depth), had to put up with the suit squeeze.
Normally, the gas used for dry suit inflation for diving is air from the primary breathing cylinder. When divers breathe helium-based gas mixes such as trimix, they often avoid inflating their suits with the helium-based gas due to its high thermal conductivity. They often carry a separate cylinder for this purpose; generally it contains air, although sometimes argon, which has lower thermal conductivity, is used. Using argon increases the insulation value of a given suit by approximately 20%, without adding any additional bulk or weight. To gain the full benefit, the user must purge the suit of air several times before each dive. Argon cylinders should always be clearly marked so that a diver does not accidentally attach a breathing regulator; this is a potential hazard especially for technical divers, who often carry several independent cylinders and regulators. Breathing pure argon will result in rapid unconsciousness. Alternatively, some trimix divers inflate their suits from a decompression cylinder containing a nitrox blend (all such decompression blends, including pure oxygen, have essentially the same thermal conductivity as air).
In surface dry suits, the wearer normally never dives deeply underwater, and is not concerned about suit squeeze or neutral buoyancy, so there are no air valves on a surface dry suit.
The P-valve 
For commercial divers or technical divers who may spend many hours in a dry suit underwater, it is not practical to have to climb back on board the ship in order to open a waterproof relief zipper and urinate. The P-valve is a urinal built into the suit, which enables a diver to urinate at any time without having to get out of the water, while keeping him or her dry and clean inside the suit.
Before putting on the dry suit, the male diver puts on a condom catheter, which is similar to a condom except that it is made of thicker material with a cuff or adhesive ring to prevent it from slipping off, and its end connects to a built-on drain tube. After putting it on, he attaches the end of the tube to a drain hose in the crotch of the suit. This drain hose leads to a vent opening just above a knee, and may also have a one-way valve (P-valve) to prevent ocean water from flowing back in if the hose gets disconnected. The female diver puts on an external catching device in the form of a wide-rimmed, low-profile, elongated cup. The rim is affixed onto the skin surrounding the labia with medical grade glue. The cup's drain hose connects to the drain hose.
Uses of dry suits 
Dry suits are often worn for boating, especially sailing, and on personal water craft in the winter months. The primary uses are for protection from spray, and in case of accidental short-term immersion in cold water if the user falls overboard. These dry suits, which are only intended for temporary immersion, are less rugged than diving dry suits. They are usually made of a breathable membrane material to let sweat permeate, keeping the wearer dry and comfortable all day. Membrane type surface dry suits only keep the user dry, and have little thermal insulating properties. Most users will wear a thin thermal undersuit, or street clothes, for warmth; but wearing ordinary fabrics can be dangerous if the suit leaks in cold water because they will lose all insulating properties.
Water sports 
Dry suits are used for windsurfing, kitesurfing, kayaking, water skiing and other surface water sports where the user is frequently immersed in cold water. These suits are often made from very lightweight material for high flexibility. Membrane type suits are commonly used in the spring and autumn with moderate water temperatures, but Neoprene and hybrid dry suits for surface sports are preferred in cold water. These provide greater thermal protection in the event of a leak. The ability to swim for self-rescue in these types of suits is important to water sports users that do not use a boat. A neoprene bottom also is less likely to allow trapped air to collect in the legs, causing the wearer to tend to float head down in the water.
Crew members who must work on the decks of commercial ships wear a type of dry suit also known as an immersion survival work suit. Single engine aircraft ferry pilots flying between North America and Europe, and helicopter pilots that must fly over the open ocean, must wear a survival suit in the cockpit, so they can continue to fly the aircraft, then exit immediately if the aircraft is ditched in cold water after an engine failure. These suits are also used on shore when working on docks, bridges, or other areas where cold water immersion is a safety risk. They are usually a three-part system consisting of:
- A warm undersuit made of synthetic fabric designed to wick moisture from sweat generated by physical exertion away from the user’s skin.
- A dry suit made with a waterproof breathable membrane to let moisture permeate out of the suit.
- A durable outer shell, designed to protect the dry suit, and to carry tools and survival gear. The outer shell may also be equipped with an inflatable bladder to give the wearer additional flotation and freeboard when immersed.
Immersion survival suits are dry suits carried for use by ship and aircraft crew who will be immersed in cold water if the craft must be abandoned. Unlike immersion survival work suits, these are not intended to be worn all the time, and are only to be used in an emergency. Survival suits will typically be a one-piece design made of fire-retardant neoprene, and optimized with quick donning features.
Dry suits are also worn by rescue personnel who must enter, or may accidentally enter, cold water. Features of dry suits designed for rescue may be a hybrid of the immersion survival and work suits, since the wearer is not expected to be working in the suit for an extended time. They may also be optimized for a specific task such as ice rescue, or helicopter rescue swimmer.
Sport diving 
Dry suits for sport diving are made in both membrane and neoprene, and primarily differ from surface dry suits in that they have inflation and deflation air valves to maintain neutral buoyancy, and are slightly more durable.
Commercial/military diving 
Dry suits for commercial and military diving tend to be much heavier and even more durable than sport dry suits because they will endure a harsh and abrasive environment, especially if being used for heavy labor work such as underwater welding. Some commercial dry suits are rated for hazardous-environment diving, and when combined with a full-face helmet can completely isolate and protect the diver from hazardous environments such as sewage pits and chemical storage tanks. These "hazmat suits" are most often made of vulcanized rubber, which is easier to decontaminate (because of its slick surface) than other, more commonly used drysuit materials.
Dry suit donning and diving hazards 
Hyperthermia on deck before a dive 
Dry suit donning is somewhat more complex and time-consuming than with a wet suit, and may require the assistance of another individual. In situations where the air is warm but the water cold, a prolonged time on the deck of a boat donning a dry suit and other gear can present a risk of hyperthermia to the preparing diver. This is of particular problem to relatively inexperienced divers, who require more time to don. This problem can be mitigated by preparing all other equipment and making sure all divers are completely prepared before fully donning the suit. It is also helpful to wet the hair and face, to allow for some cooling while on deck.
Seal damage 
Latex seals are easily pierced by sharp objects. Gripping the seal with long fingernails to pull it on or off can cut through the material, while long toenails can damage thin rubber booties when the foot is pushed inside tight-fitting fins.
Latex is subject to rubber perishing, or "dry rot," where ozone normally present in the air deteriorates the material over time, regardless of use. A latex seal is generally expected to last 1–2 years. The useful life can be extended by coating the seals with a special protective compound, and (in suits with removable seals) detaching the seals when not in use and keeping them in airtight containers. They should also be kept in a cool, dark environment.
Latex seals are somewhat elastic, but can be easily torn if overstretched. Powdered talc can help the seals slide on easier.
Neoprene seals are a less popular alternative. They are less watertight than latex, but are much more resistant to dry-rot although they cannot be repaired as easily by the user.
Zipper damage 
Waterproof zippers need the two rows of open teeth to be reasonably lined up in front of the pull, for the zipper to slide without excessive effort. (Because of their construction waterproof zippers need two or three times as much pull as regular zippers to close.) It is best to hold the opening together as the zipper is pulled shut to prevent misalignment which can permanently damage the sealing edge. For this reason zippers across the back of the shoulders or down the back of the suit are almost impossible for one person to close properly by themselves, and yanking harder to try to force the unreachable zipper closed often just results in misalignment and permanent zipper damage.
Suit damage 
Damage to the lower part of the suit can cause a sudden inrush of very cold water for winter users, or an inrush of hazardous chemicals for commercial inspection divers.
Damage to the upper part of the suit can cause a sudden venting of the air, resulting in a total loss of thermal insulation in membrane suits and sudden uncontrolled descent, followed by water/chemicals seeping in.
Dry suits pose their own unique problems compared to wet suit diving, due to the complex construction and since a diver needs to constantly manage and adjust the air volume inside the suit. During descent, air must be added to maintain constant volume. This prevents suit squeeze, loss of neutral buoyancy, and potential uncontrolled descent. During ascent, such air added at depth must be removed again, in order to prevent ballooning, loss of neutral buoyancy, and potential uncontrolled ascent. Most modern dry suits are equipped with automatic spring-loaded exhaust valves, which can assist with this problem when properly set.
Diving without a BCD 
Since the dry suit can contain air, some divers control their buoyancy with the dry suit and dive without the usual BCD / buoyancy control device that is commonly worn by wet suit divers. Although it is possible to dive like this, the risks are higher than when using a buoyancy compensator.
Dry suits are generally more easily damaged and prone to failure. The provided buoyancy is less reliable than buoyancy compensators, and dry suits can flood when punctured. Wrist and neck seals can vent easily without the diver wanting them to vent; a trivial problem during normal diving but more serious in an emergency or with an incapacitated diver. If the diver is over-weighted, the suit may contain additional air to offset the extra weight; migration of this air, particularly to the legs when the diver is not upright, can cause the diver to "invert" to a legs-up position that makes venting the drysuit difficult (see more on this problem, in the following section below).
Buoyancy compensators air bladders are generally are more robust and reliable than dry suits. They are designed for life-saving both at the surface and underwater. They provide buoyancy only at the top of the body, where it usefully keeps the diver upright. In addition, the vent valves of a BCD are more secure, requiring the diver to press a button to release buoyancy.
Carotid-sinus reflex 
An over-tight neck seal can put pressure on the carotid artery, causing a reflex which slows the heart, resulting in poor oxygen delivery to the brain, light-headedness and eventual unconsciousness. For this reason, neck seals should be stretched or trimmed to the correct size.
Accidental body-inversion hazards 
If there is more air in the dry suit than is needed to counteract "squeeze" on the undersuit, that excess air creates a "bubble" which moves to the highest point of the suit; in an upright diver this is the shoulders. In such cases, divers wearing loose baggy suits need to keep their legs at level or below their waist. Otherwise the bubble quickly moves to the highest point, and if the legs are above the waist, the bubble moves into the legs and feet, causing the legs to rise, and "inverting" the diver's body into a head-down position.
The movement of a such a large bubble to the legs can be a problem for a number of reasons: It balloons the legs, and it may inflate thin rubber booties enough to cause fins to pop off; a diver without fins has more restricted ability to move and become upright, and also loses the ability to kick downward to maintain depth, so that the bubble expansion problem does not grow worse. Movement of gas into the legs and feet may also cause special difficulties in drysuits that have air exhaust values only at the shoulders or wrists, because the air in the legs and booties cannot be evacuated while the diver is inverted, and such a diver may be moving toward the surface, causing the problem of expanding air in the suit to grow worse with each meter of lost depth. (Some low-quality buoyancy control devices also cannot vent air, when inverted). If the diver is positively buoyant and rising, the buoyancy of the dry suit becomes uncontrollable after rising though a certain fraction of depth, and there is then an increased risk of a rapid ascent which grows more rapid, as the distance to the surface decrease. The final result of such a run-away inversion is a diver rising all the way to the surface, feet first, in an uncontrolled ascent that is too rapid for decompression safety.
When the suit is being used correctly, the bubble inside it is relatively small, and its movement is not important. The bubble may be large for a variety of reasons: if a diver has ascended without venting the suit; if the valve supplying gas to dry suit fails in the open position; or if the diver is over-weighted, and extra air has been added to the suit at some point to make the diver neutrally buoyant. The size of the bubble can be minimised by being correctly weighted and venting excess gas from the suit on ascent. Some divers ensure that the bubble remains at the top of their body by using the buoyancy compensator to counteract any excess weighting, keeping only the minimum gas necessary to avoid squeeze inside the drysuit.
The recommended solution in all such "inversion accidents," is for the wearer to bend at the knees and powerfully flap the arms to do a backward or forward roll to the upright position and then vent the suit, if needed, by manually opening the neck seal (sometimes called "burping the suit") by breaking the seal-neck contact with a finger.
Surface dry suit users can face a similar inversion problem. The problem is more acute when not wearing a personal flotation device (life vest) over the dry suit. For surface dry suit users, the inversion can be much more critical if no one is nearby to assist, since the wearer may be held upside down and unable to breathe, and may also have water run down into their nose while inverted.
It is not a problem for close-fitting neoprene suits, or hybrid suits with neoprene bottoms, which prevent air from easily moving into the legs of the suit. Wearers of baggy surface dry suits can mitigate the problem by venting out as much excess air as possible before entering the water. This is typically done by crouching down and leaning forward, wrapping the arms around the knees, and then having an assistant zip the suit shut while it is stretched out tightly. Excess air can also be "burped" out of the neck seal.
Gaiters and ankle weights 
Some baggy suits have elastic "gaiters" that can be pulled snug around the legs to help prevent an inversion event from happening. Small lead ankle-weights (typically one or two pounds) on velcro straps can also be used with any dry suit, both to provide extra weight at the bottom of the suit, and to constrict the ankle and calf region of suit once the foot is in the boot, so that the size of the bubble that can accumulate in the lower legs of the suit in the event of an inversion, is limited.
Early examples of dry suits 
These suits are all the membrane type.
|Maker||Make||1/2 piece?||When available||Notes||Info link|
|Pirelli||Pirelli Diving Suit||2||from 1930s||designed for Italian frogmen|||
|Siebe Gorman||"Frogman" suits||1 or 2||World War II & after||designed for British frogmen
|Spearfisherman||Spearfisherman Frogman Suits||2||1945 & after||designed for USA frogmen|||
|U.S. Divers||U.S. Divers Seal Suit||1 or 2||from 1953 or before||varIous|||
|Heinke||Heinke Delta Suit||2||from mid-1950s||rubberized stockinette|||
|Healthways||Healthways Carib Suits||2||from 1955 or before||pure natural rubber|||
|Bel-Aqua||Bel-Aqua Dry Suits||1
|from 1955 or before||a 3-ply material, front tube entry
a 3-ply material
|unidentified||Seamless Suits||2||from 1953?||dipped pure latex|||
|made by or for Lillywhites||Lillywhites Mid-1950s Suits||2||from 1955 or earlier||rubberized stockinette|||
|So-Lo Marx Rubber Company||Skooba-"totes" Suits||2||from late 1950s||all-rubber|||
|Siebe Gorman||Siebe-Heinke Dip Suit||2||1964 & after||dipped latex|||
See also 
|Look up drysuit in Wiktionary, the free dictionary.|
- Piantadosi, C. A.; Ball D. J., Nuckols M. L., and Thalmann E. D. (1979). "Manned Evaluation of the NCSC Diver Thermal Protection (DTP) Passive System Prototype". US Naval Experimental Diving Unit Technical Report. NEDU-13-79. Retrieved 2008-04-21.
- Brewster, D. F.; Sterba J. A. (1988). "Market Survey of Commercially Available Dry Suits". US Naval Experimental Diving Unit Technical Report. NEDU-3-88. Retrieved 2008-04-21.
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