There are few soft floor coverings that are guaranteed against shrinkage; therefore, dimensional changes of your rug should be expected during cleaning. Your skilled professional rug cleaner takes every step economically possible to minimize this inherent characteristic.
During the spinning and weaving process, fibers and fabrics must be kept under tension for proper functioning of equipment. For example, warp yarns are held under tension on a loom during a rug's construction. Stretching occurs during this and other operations and fibers and fabrics remain stretched until moisture causes them to relax. Shrinkage at this point is often referred to as relaxation shrinkage.
The amount of shrinkage that can be expected will depend upon the construction of the rug and the fibers used in the backing. Most shrinkage is due to the type of backing fibers used. The density of the face fibers will also have a bearing on the amount of shrinkage. The type of face fiber has no relation to the amount of shrinkage.
Shrinkage that causes dimensional changes results entirely from wetting the backing yarns. Moisture causes the fibers to swell and this forces the weave threads to contract, causing the overall floor covering to shrink. Most of this type of shrinkage will occur during the first thorough wetting (usually the first cleaning).
On some rugs, as much as ten percent shrinkage will take place. It is more realistic to see about two percent shrinkage of the average rug.
Shrinkage can also take place in the home due to the rug's backing yarns absorbing moisture from humid air.