A process for stabilising a natural or synthetic organic polymer or copolymer obtained from a water based latex or emulsion of the polymer or copolymer comprising adding to the later or emulsion prior to coagulation of the polymer or copolymer a substantially water-free self-emulsifying liquid stabiliser mixture comprising (a) a phosphite or phosphonite stabiliser; (b) a phenolic antioxidant and (c) an emulsifying agent. The preferred stabiliser package is a blend of 2 parts by weight liquid phosphite stabiliser to 1 part by weight liquid phenolic antioxidant which has dissolved in it a fatty acid ester emulsifier.