A potting compound is used to embed delicate or coordinated instruments within a casing to protect them from shock or vibration which would destroy them or derange them. The essential ingredients of the potting compound are dihydroxypolybutadiene, an extender oil, a microfine polypropylene powder, and an organic diisocyanate. The resulting compound is presumed to have an oil-modified polyurethane structure as a matrix enclosing the polypropylene powder as an integrated, dispersed phase. The compound has high adhesion to practically everything used in potting, requires no interlayer, is flexible at -65.degree. F. and is heat resistant for short periods at 260.degree. F.