COLSON Hi-Tech Polyurethane Wheels feature a polyurethane tread that is bonded to a polyolefin core. Choose standard (03) models or industrial strength (06) models with ribbed polyolefin core that adds strenght for loads subjected to shock and hard impacts. Tread is molded in and around and through the core to prevent separation. Resists most chemicals, solvents, water and acides. Red tread with gray core.