A colourless crystalline compound, C4H8N8O8; r.d. 1.9; m.p. 276–286°C. It has a structure similar to that of cyclonite (RDX), but with an 8-membered ring rather than a six-membered ring. An extremely powerful explosive, it is used mainly for military purposes and as a rocket propellant. The name comes from ‘High Molecular Weight RDX’.