A reed is part of a loom, and resembles a comb. It is used to push the weft yarn securely into place as it is woven, separates the threads and keeps them in their positions, keeping them untangled, and guides the shuttle as it moves across the loom. It consists of a frame with lots of vertical slits. The reed is located inside the beater. Floor looms and mechanized looms both use a beater with a reed, whereas Inkle weaving and tablet weaving do not use reeds.
Modern reeds are made by placing flattened strips of wire (made of carbon or stainless steel) between two half round ribs of wood, and binding the whole together with tarred string. Historically reeds were made of reed or cane, however modern reeds are made of metal wires. John Kay in 1738 first used flattened iron or brass wire, and the change was quickly adopted. Previously the cane was split by pressing it against a spindle that had knives radiating out of it at the appropriate distance apart. The split cane was then bound between the ribs of wood in the same manner as the wire is now.
The wire is flattened by passing it through rollers, and then straightened. Next it is cut to a uniform width, given rounded edges and smoothed. The final step is to cut the long wire to the correct length and insert it into position. The tarred cord that binds the reed together is wrapped around each set of wooden ribs and between the dents to hold the ribs together.
The length of the metal wire varies depending on the type of fabric and the type of loom being used. For a machine powered cotton loom, the metal wires are commonly 3.5 inches (89 mm) long. For hand powered floor looms, around 4 inches is common.
Both the wires and the slots in the reed are known as dents (namely, teeth). The warp threads pass through the dents after going through the heddles and before becoming woven cloth. The number of dents per inch determines the fineness of the cloth. One or more warp threads go through each dent. The number of warp threads that go through each dent depends on the warp, and it is possible that the number of threads in each dent is not constant for a whole warp. The number of threads per dent might not be constant if the weaver alternates 2 and three threads per dent, in order to get a number of ends per inch that is 2.5 times the number of dents per inch, or if the thickness of the warp threads were to change at that point, and the fabric to have a thicker or thinner section.
One thread per dent is most common for coarse work, for finer work (20 or more ends per inch) two or more threads are put through each dent. Threads can be doubled in every other space, so that a reed with 10 dents per inch could give 15 ends per inch, or 20 if the threads were simply doubled. Also, threads can be put in every other dent so as to make a cloth with 6 ends per inch from a reed with 12 dents per inch. Putting more than one thread through each dent reduces friction and the number of reeds that one weaver needs, and is used in weaving mills. If too many threads are put through one dent there may be reed marks left in the fabric, especially in linen and cotton.
For cotton fabrics reeds typically have between 6 and 90 dents per inch. When the reed has a very high number of dents per inch, sometimes there are actually two rows of wires which are offset. This is to keep loose fibers from twisting and blocking the shed.
In order to weave many different patterns on the same loom different reeds are useful. Modern floor looms and several other types of loom use interchangeable reeds, with a different number of dents per inch. The most common sizes available for the hand-weaver are 6, 8, 10, 12, or 15, though more are made, and sizes between 5 and 24 are not uncommon. The finer the reed, the more dents per inch, and, in general, the more ends per inch in the final woven fabric. This is because by beating the weft into place the reed determines the distance between threads, or groups of threads. Having interchangeable reeds allows a weaver to do many different types of weaving on the same loom. By changing the reed the weaver can move from weaving fine fabric to coarse fabric without needing a different loom.
Reeds also come in different widths. The width of the reed determines the maximum width of the warp.
Sleying the reed 
Sleying is the term used for pulling the warp threads through the loom, which happens in the warping process (the process of putting a warp on the loom). Sleying is done by inserting a reed hook through the reed, hooking the warp threads and then pulling them through the dent. The warp threads are taken in the order they come from the heddles, so as to avoid crossing threads. If the threads cross, the shed will not open correctly when the weaving is begun.
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