The Performance TPR (Thermal Plastic Rubber or TPE for Thermal Plastic Elastomer) Wheel is specially engineered to provide unsurpassed durability and reliability. This premium wheel combines the durability of a hard tread wheel with the quiet floor protection of a soft tread wheel. They are made of a thermoplastic elastomer which is permanently bonded to a polypropylene core and will not mark floors. The Performance TPR wheel is resistant to chemicals, acids, bases, alcohols, salts and steam. The Performance TPR Wheel tread material can be made to various durometers. The Performance Wheel is available with a flat tread to provide maximum load surface or round tread to provided easy turning. Round tread is only available on the 6? x 2? and 8? x 2? wheels.