Foundation refers to the basic structural components of handmade rugs. These components consist of warps and wefts.

Warp
Warps are vertical strands of fiber which stretch from the top to the bottom of the rug. Warps are an extremely important component because the knots are tied to them and the weft strands are passed (woven) through them. Even tension of all warp strands is essential in producing a rug without wrinkles. The extensions of warp strands are rug fringes. Fringes are knotted at the ends to ensure that the wefts and the knots do not unravel.

Warp Strands

Warp Strand Extensions (Fringe)

Weft
Wefts are horizontal strands of fiber that are passed (woven) through the warp strands. Unlike the warps, wefts are not structured prior to weaving. They are added before and in between the rows of knots to secure the knots in place. Each side of the rug, where the wefts begin and end, is called selvedge.

Beating Weft Strands with Comb to Secure Knots in Place

Right Side Selvedge

Foundation Material
In general, the same material is used for both warp and weft, and it is often cotton. Wool is used as a foundation material in some nomadic and village rugs because wool is readily available to these weaving groups. Silk is generally used in foundation of rugs with silk piles. Rugs with silk foundation and pile are very exceptional and expensive. These rugs are light in weight and are very finely knotted. Silk is a very good foundation material because it is very strong and keeps its shape.