Two sets of yarns, called the warp and the woof (more commonly filling, or weft) are used in weaving, which is carried out on a mechanism known as a loom. Warp yarns run along the length of the loom; filling yarns run across it. The warp is wound on huge reels, called beams or creels, that are placed at the feet of the loom, and the warp yarns are threaded through the loom to form a series of parallel threads. The filling is fed from the side of the loom by bobbins, which are changed either automatically or manually when the yarn runs out. The loom shuttle carries the filling yarns across the loom, interlacing them at right angles with the warp yarns. Different patterns and textures are achieved by varying the number of warp yarns and by altering the sequence in which they are raised or lowered. A temporary protective coating known as sizing protects the warp yarns against damage during the weaving operation.