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1. A flexible polyurethane foam having a density of 25-70 kg/m3, a compression load deflection at 40% (CLD) of 5-15 kPa, a volume increase at water saturation of at most 25%, and a water buffer capacity of 40-60% obtained by reacting at an isocyanate index of 20-70 and at a water index of 200-400 the following compounds
a polyisocyanate prepolymer having an isocyanate-value of 20-30% by weight and made by reacting a polyisocyanate comprising 30-80% by weight of diphenylmethane diisocyanate and 20-70% by weight of homologues of diphenylmethane diisocyanate the homologues having an isocyanate functionality of 3 or more, the amounts both calculated on the amount of polyisocyanate, and a polyol used to form the prepolymer having oxyethylene groups in an amount of at least 50% by weight, calculated on the weight of the polyol used to form the prepolymer, wherein the polyol has an average molecular weight of 250-800; a polyoxyethylene polyoxypropylene polyol or a mixture of polyoxyethylene polyoxypropylene polyols, said polyoxyethylene polyoxypropylene polyol or said mixture of polyoxyethylene polyoxypropylene polyols having an average nominal hydroxyl functionality of 2-4, an average molecular weight of 2000-8000 and an average oxyethylene content of 25-50% by weight, calculated on the weight of said polyoxyethylene polyoxypropylene polyol or said mixture of polyoxyethylene polyoxypropylene polyols respectively; water; optionally, isocyanate-reactive chain extenders having an average molecular weight of 60-1999; optionally, isocyanate-reactive cross-linkers having an average molecular weight of 60-1999 and; optionally, in the presence of auxiliaries and additives. |
