Layered clothing

Layered clothing is a manner of dressing using multiple garments that are worn on top of each other. Some of the layers have different, largely non-overlapping, functions. Using more or fewer layers, or replacing one layer but not others, allows for flexible clothing to match the needs of each situation. Two thin layers can be warmer yet lighter than one thick layer, because the air trapped between layers serves as thermal insulation.

Layered clothing is particularly relevant in cold climates, where clothing must at the same time transfer moisture, provide warmth, and protect from wind and rain. In a hot and dry climate, clothes have very different functional requirements: they must block the radiation from the Sun, and allow for sufficient air circulation. Therefore, layered clothing in the sense used in this article is largely irrelevant to hot and dry climates.

Outdoor and sports wear manufacturers favor layered clothing because, among other reasons, it allows them to offer so-called "technical" or "functional" clothes which are optimized for the particular demands of a specific layer. Such clothes are often made of advanced synthetic materials, and can be expensive.

Layers

Usually at least three layers are identified as follows:

• Inner layer provides comfort by keeping the skin dry. Also called base layer or first layer.
• Mid layer provides warmth. Also called insulating layer.
• Shell layer protects from wind and water. Also called outer layer.

Often clothes combine two adjacent layers, as in the case of warm undergarments that provide both comfort and insulation.

Inner layer

The purpose of the inner layer is to draw the sweat away from the skin to the next layers, which makes the wearer feel warmer and more comfortable. The transfer of moisture happens due to capillary action. This is sometimes called wicking, and thus the used materials are called wicking materials. When moisture has moved from the skin into (nonabsorbent) clothing, it has more surface area and will evaporate faster. If a piece of clothing does not transfer moisture well, it is not strictly an inner layer garment at all, but simply a comfortable mid-layer garment.

• Synthetic materials such as polyester and microfiber-based fabrics are good choices as they do not absorb moisture but may transfer it well. They can also carry specialist finishes, such as anti-bacterial agents which reduce odours, and insect repellent.

• Wool has fairly good wicking properties. How comfortable wool feels against skin varies greatly, from very rough and itchy to comfortable. Wool doesn't start to smell as quickly as synthetic materials.

• Silk feels comfortable, but is weaker than and harder to take care of, and is less commonly used.

• Cotton is cheap and feels comfortable when dry but absorbs moisture easily and is slow to dry out, especially in cold conditions. Cotton is better suited for the middle layer.

Mid layer

The mid layer is needed in cold weather to provide additional insulation. For maximum warmth, multiple thin mid layers can work better than one thicker layer. The use of multiple thin layers also facilitates adjustment of warmth. The mid layer should be more loose-fitting than the inner layer, as this leaves insulating air between the layers. However, if best possible moisture transfer is desired, too great a gap between any adjacent layers of clothing may reduce the moisture transfer by capillary action from one piece of clothing to another. On the other hand, very loose-fitting layers can allow more removal of moisture (and heat) via air circulation.

• Wool is the traditional mid layer material with several good properties: it has good insulation even when wet, absorbs moisture but does not feel wet even when it holds significant moisture, and transfers moisture.

• Fleece made from PETE or other synthetics has many of the features of wool, but is lighter. It provides good insulation even when wet, absorbs very little moisture, and dries quickly. Although no longer commonly used in the industrialized world, natural sheepskin fleece could also serve the mid layer function.

• Down has a very good warmth:weight ratio, and can be packed down (squeezed) to take very little room. On the downside, it is expensive, makes a thick garment, dries slowly, loses its insulating properties when wet or compressed, and stops lofting properly after being washed several times.

• Synthetic Fiberfill such as polyester fiber is used similarly to down, but does not have as good a warmth:weight ratio. However, it is less expensive, provides good insulation even when wet, dries quickly, and absorbs very little moisture. Thinsulate is a brand of very fine fiberfill that provides higher warmth for a given thickness.

• Cotton, as with the inner layer, is a cheap alternative, but a reasonable choice only when low insulation and moisture transfer is needed.

Shell layer

A waterproof breathable (hard shell) jacket

The outermost clothes are called the shell layer, but only if they block wind or water, or have good mechanical strength. Ideally the shell layer lets moisture through to the outside (that is, is breathable), while not letting wind and water pass through from the outside to the inside. While this is enabled to some degree by modern materials, even the best and most expensive materials involve a trade-off between breathability and water- and wind resistance.

If heavy sweating is expected, one should avoid wearing any shell layer garments unless their protective properties are essential. For example, when one is jogging, no shell layer is likely to be able to transfer enough moisture to keep the wearer feeling dry. Instead, one should consider using sufficiently warm mid layer clothes.

• Plastic raincoats protect completely from water and wind, but let through no moisture. To compensate for that, such raincoats usually have flap-covered holes and are very loose-fitting at the bottom to allow air circulation.

• Waterproof breathable (hard shell) materials are waterproof and somewhat breathable. Their essential element is a thin, porous membrane that blocks liquid water, but lets through water vapor (evaporated sweat). The more expensive materials are typically more breathable. The best-known brand is Gore-Tex.

• Water resistant (soft shell) materials block water only partially. On the other hand they are usually more breathable and comfortable, thinner, and cheaper than completely waterproof materials. Water-repellent coatings are often used. Before waterproof-breathable shells were invented, the "60/40" (60% cotton, 40% nylon) parka was widely used. Soft shells are not water "proof".

The term Soft Shell is increasingly used to describe garments that combine partial water resistance with partial wind breaking ability. Soft shell fabrics come in numerous varieties with many garments offering a combination, such as a wicking layer. In many cases insulation is combined in an attempt to replace several layers with a single highly flexible one.

Adjusting a layering system

As the intensity of exercise or environmental conditions change, the amount or quality of layers worn should be changed. In particular, if clothes become wet from sweating during heavy exercise, they can be much too cold during the following period of rest. Below are two basic strategies for this problem.

Vents

Some clothes feature adjustable vents, such as below armpits. The positioning and design of the vents allow for area specific cooling while only marginally reducing exterior moisture resistance.

Removing layers

Removing the shell layer during heavy exercise can pose problems if the clothes underneath lack required mechanical strength or water proofing. In such situations, using a mid layer with enough of the required shell layer properties can be a good choice.

Fashion use

Combining different garments in layers can be used to create a variety of outfits. This provides similar practical benefits to practical layering, in that the wearer can shed layers according to changes in temperature, and is also a way of making use of clothing to produce different looks and mix colours in various ways.

See also

• Waterproof fabric
• Durable Water Repellent
• Heated clothing

External links

• A scientific approach to layering for hikers and mountaineers
• Learning to Layer Clothing
• ABC of Hiking