Like other tertiary amines, it catalyzes the formation of urethane foams and epoxy resins. Epoxy/urethane systems are also topical film membranes. There are typically four classes of conformal coatings&colon; Acrylic, Urethane, Silicone, and Varnish. Trivex is a urethane based pre-polymer. The reaction of PPD with phosgene gives the diisocyanate, a precursor to urethane polymers. The tentacles were created out of a combination of silicone and urethane. The durometer of a wheel is how hard the urethane is. The photo below on the right shows crimson clover sprouts grown on urethane foam mats. Almost all longboard wheels are made from urethane. The urethane decomposed with age, making the pads unusable. The flight surface is also sprayed with urethane, which can support VTOL jets, like Harriers. Additional front suspension enhancements come from new urethane bump stops, two per side. The options list was updated to include a urethane bumper for impact improvement. Powell became interested in skateboarding again, as he realized urethane wheels improved a skateboard's ride. The name bethanechol refers to its structure as the urethane of beta-methylcholine.