An area rug having an upper loop or pile surface and a secondary backing having a thin, open cell urethane backing adhered thereto to lessen the tendency of the area rug to crawl on the undersurface while maintaining total thickness no greater than 10% greater than the thickness of the primary rug....http://www.google.com.au/patents/US4286003?utm_source=gb-gplus-sharePatent US4286003 - Thin polyurethane foam backed rug
