Four hydroxy-terminated poly( dimethyl siloxane) (HTPDMS) prepolymers of varying viscosities and molecular weights were prepared and used with and without alumina trihydrate as a filler. The HTPDMS viscosity and filler percentage were optimized to ensure acceptable pot life and mechanical properties. Low nitroglycerine migration from the propellant to the inhibitor, excellent temperature stability, and good bonding between the propellant and inhibitor at temperature extremities (-40 to +60 degrees C) are some of the remarkable features of a room-temperature vulcanizing (RTV) silicone inhibitor. Double-base (DB) propellant grains were inhibited by a casting technique using Siloxane-15 and statically fired in a rocket motor. A smooth pressure-time profile infers that Siloxane-15 works satisfactorily as an inhibitor for DB propellants.