The basic material used in this work was a low-molecular-weight polybutadiene with isocyanate endgroups in the main chain. The isocyanate groups were used for crosslinking of the oligomeric polybutadiene with glycerol as a three-functional crosslinker. The prepared polybutadiene-based polyurethane gel was subsequently vulcanized with sulphur. The effect of sulphur content on mechanical and electrical properties of resulting materials was investigated with the aim to find an optimum matrix composition for the preparation of composite materials. Several types of glass fiber fabric reinforcement differing in fabric weight and fabric ply thickness were tested. Mechanical properties of composites based on the optimum matrix composition and different types of glass fibers were measured and compared. Being vulcanized with sulphur, the polybutadiene was found to possess improved mechanical properties and retain an excellent electroinsulating character. Moreover, the sulphur-vulcanized polybutadiene was proved good as a matrix for the preparation of glass fiber-reinforced composite materials having enhanced tensile and flexural properties. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3446-3452, 2011