Authentic Oriental Rugs always use natural fibers in the foundation material, which is not surprising when you consider their origin and history.
The foundation of Oriental Rugs is made up of weft and warp. The pile is the face of the rug.
Weft: the horizontal threads usually made up of cotton, wool or silk. The color of the weft has no bearing the color of the actual rug. Weft is only visible on the back of the rug.
Warp: the vertical threads usually made up of cotton, wool or silk. The warp of the completed rug is what makes up the fringe, but weavers sometimes add extra fringe material to the ends of the rug.