Polyurethanes are often vacuum cast to ensure void-free parts. The process calls for a mold to be placed in a vacuum chamber and the mixed resin system injected under a vacuum of 20 to 25 inches of mercury until the mold is completely filled. The vacuum is then released and the part is allowed to cure. Vacuum-cast polyurethanes are ideal for prototyping medical equipment and models, clear lenses, furniture and automotive components.

Polyurethanes designed for use in vacuum casting have the following properties:

• Low viscosity
• Shore A hardness systems exhibit good elongation and tear strength for producing flexible gaskets, seals and fixtures and for overmolding rigid plastics
• Shore D hardness products include white, clear, translucent and tan systems that are colorable and feature properties such as flame retardance, heat resistance, high flexural modulus and high impact strength