Hydroxyl-terminated polybutadiene

Hydroxyl-terminated polybutadiene (HTPB) is a polymer of butadiene terminated at each end with a hydroxyl functional group. It belongs to a class of polymers known as polyols. It is used to react with a diisocyanate to form a polyurethane, a stable and easily stored synthetic material.

Physical properties
HTPB is a clear, viscous liquid. The properties cannot be precisely stated, because HTPB is manufactured in various grades to meet specific requirements. HTPB is thus a generic name for a class of compounds.

Uses
HTPB is used to bind the fuel and oxidizer into a solid mass for solid rocket motors. It is also used as a hybrid rocket fuel. Together with N2O (nitrous oxide, or "laughing gas") as the oxidizer, it is used to power the SpaceShipOne hybrid rocket motor, developed by SpaceDev. It also powers all 3/4 stages of the Japanese M-5 rocket satellite launchers. JAXA describe the fuel as "HTPB/AP/Al=12/68/20" which means, proportioned by mass, HTPB 12% (binder and fuel), Ammonium perchlorate 68% (oxidizer), and Aluminium powder, 20% (fuel).