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.