HTPB is a translucent liquid with a color similar to wax paper and a viscosity similar to corn syrup. The properties vary because HTPB is a mixture+ rather than a pure compound+, and it is manufactured to meet customers' specific requirements. A typical HTPB is R-45HTLO. This product consists of oligomeric units typically containing 40–50 butadiene molecules bonded together, with each end of the chain terminated with a hydroxyl [OH] group:
R-45HTLO has a functionality+ of 2.4-2.6, which means that there is (approximately) one additional hydroxyl group located along the chain for every two oligomeric units. This provides side-to-side linkage for a stronger cured product. HTPB is usually cured by an addition reaction+ with di- or poly-isocyanate+ compounds.
Polyurethanes prepared from HTPB can be engineered for specific physical properties; polyurethanes may be highly elastic or tough and rigid. Some products include: rigid foam insulation panels; durable elastomeric wheels and tires (used for roller coaster+s, escalator+s, skateboards+, etc); automotive suspension bushings+; electrical potting compounds; high-performance adhesive+s; surface coatings and surface sealants; synthetic fibers+ (e.g., Spandex+); carpet+ underlay; hard-plastic parts (e.g., for electronic instruments).
An important application of HTPB is in solid rocket propellant+. It binds the oxidizing agent+ and other ingredients into a solid but elastic mass. The cured polyurethane acts as a fuel in such mixtures. For example, HTPB is used in all 3/4 stages of the Japanese M-5 rocket+ satellite launchers and PSLV+ rocket developed by ISRO+ for satellite launches. JAXA+ describes the propellant as "HTPB/AP/Al=12/68/20", which means, proportioned by mass, HTPB plus curative 12% (binder and fuel), ammonium perchlorate+ 68% (oxidizer), and aluminium+ powder 20% (fuel).