Molded on polyurethane wheels use a non-marking polyurethane tread that is chemically bonded to a cast iron core. Polyurethane wheels resist flat spots on the tread from long periods of standing. Equal in strength to a cast iron wheel, but also floor protective, resistant to oil, grease, water, and many solvents, and easier rolling. construction. Wheel tread hardness of 90-95 Shore (A) Durometer. For more caster options, including bearings and top plates, please call our sales team in West Reading, PA, at 1-800-215-8220.