Urethane rollers. Low profile, 7/8" floor clearance. Surface is resistant to solvents, greases and fuels. Dimensions: Length 38", Width 17-1/2", Height 4" This has a unique design that is body fitting. It was developed through testing on many body types to provide optimum comfort. Also its 2" longer for a better fit. The rollers are inserted into the creeper body. This provides added strength and easy roller replacement. The creeper itself is simple to clean.