Abstract: The invention relates to a waterproof sheet material, suitable for use as a waterproof roofing layer, as a bridge deck or like waterproofing material, and as a dampcourse material, the sheet being composed of a mixture comprising (a) a bituminous material, (b) a synthetic polymeric material, and (c) particulate filler, said synthetic polymeric material comprising at least one uncured copolymer selected from ethylene-propylene copolymers and ethylene-propylene-diene copolymers and at least one synthetic polar elastomer. The sheet material may contain ethylene-vinyl acetate copolymer, and plasticizer, fire-retardant, and minor additives such as antioxidants may be incorporated. A suitable synthetic polar elastomer is nitrile rubber. The sheet material maintains good performance properties under low temperature conditions.