Polyurethane is mechanically bonded to a high-density polypropylene core in this Urethane on Polypropylene Wheel, which provides this product with a number of benefits. This mechanical bond eliminates bond separation due to wet conditions, and the combination of both materials provides for a long-lasting, long-wearing industrial wheel that is impervious to water (including saltwater), as well as resistant to oils, grease, and most solvents and chemicals. Urethane on Polypropylene Wheels are very popular, attractive, lightweight, and extremely durable wheels used in countless applications.