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, it also separates the warp threads and holds 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 securely held by 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 to a uniform thickness by passing it between rollers, straightened, given rounded edges and smoothed. The final step is to cut the 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 (100 mm) 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 (or per cm or per 10 cm) indicates the number of gaps per linear width, the number of the warp thread ends by weaving width determines the fineness of the cloth. One or more warp threads may 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.