A carpet consists of two parts: one is "foundation", which is formed by warp and weft yarns and the other is the "pile".
Warp yarns are the vertical strands of fibers stretching from the top to the bottom of a carpet. They are extremely important components because the knots are tied to them and the weft yarns are woven through them. Generally, if the warp yarns are not evenly and tightly woven, a carpet is easily to get wrinkled.
Weft yarns are the horizontal strands that stretch from the left to the right side of the carpet.
They are woven through the back and front warp yarns and added before or after the rows of knots, to prevent them from becoming loose. Usually the warn and weft yarns use the same fiber i.e. cotton, wool or Silk in hand-made carpets. Cotton is most widely used due to its lowest cost but wool is still quite popular in places where it is readily available. Silk is the most expensive one but it's quite strong and elegant and thus is highly recommended as the foundation for high quality carpets.
The "pile" forms the designs and patterns and in effect is the 'working surface' of the completed carpet. It is the upright end of strand which is shaped by the knots that may be cut or looped.
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