Carpet consists of dyed pile yarns; a primary backing in which the yarns are sewn; a secondary backing that adds strength to the carpet; adhesive that binds the primary and secondary backings; and, in most cases, a cushion laid underneath the carpet to give it a softer, more luxurious feel.
Ninety-seven percent of pile yarns today are made up of synthetic polymers; the rest of the yarns are wool and comprise the more expensive, woven carpet. Synthetics are plastics such as nylon (which is in 66% of all carpet), acrylics (15%), polyester (less than 15%), and polypropylene (less than 5%). These pile yarns are dyed using a variety of organic chemical compounds, or occasionally, organometallic complexes.
Both the primary and secondary backing are largely made of woven or nonwoven polypropylene, though some secondary backing may still be made of jute, a natural fiber that, when woven, looks like burlap. The adhesive used to bind the backings together is almost universally synthetic rubber latex. The most common padding is rebond (bonded urethane), though various forms of synthetic latex, polyurethane, or vinyl might be used instead. Rebond is recycled scrap urethane that is chopped into uniformly sized pieces and pressed into layers. Although rare, some carpet cushioning is made up of horse hair or jute. A plastic top sheet is usually added to the top to insure a smooth surface against the carpet.