A fragmentation warhead device has a fabric liner woven from high-strength fibers located between the explosive charge and the fragments. The liner has a maximum diameter larger than that of the overall warhead, and is compressed to fit closely around the explosive charge prior to detonation by forming one or more longitudinal folds or pleats in the fabric. The fragments are retained against the outer surface of the sleeve prior to detonation by a suitable outer enclosure, and may be located between adjacent pleats in the fabric. On detonation, the sleeve expands to contain the gases produced by the explosion for an extended period of time.