Abstract: Organopolysiloxane compositions adopted for easy conversion into burn resistant foams useful, e.g., for the protection of nuclear power installations, include admixture of various organopolysiloxane polymers comprising SiH, SiOH, SiR.sub.3 and Si-vinyl functions, and notably a hydroxylated liquid resin containing CH.sub.3 SiO.sub.1.5 and (CH.sub.3).sub.2 SiO units, or reaction product of a hydroxylated MQ resin with a hydroxylated polyorganosiloxane oil, or mixture thereof.

Abstract: A flexible, elastic, uniform polyurethane foam is cold foamed and set from a composition of matter comprising (i) a polyisocyanate, (ii) a polyether-polyol having a molecular weight ranging from 800 to 50,000 and at least 2.1 hydroxyl radicals per mol, of which hydroxyl radicals at least 35% are primary hydroxyl radicals, (iii) a stabilizing amount of an organosilicon stabilizer therefor, and (iv) a blowing agent; said organo silicon stabilizer being a triorganosilylated polypentaerythritol having the structural formula:(R.sub.3 SiOCH.sub.2).sub.4-a C{CH.sub.2 OCH.sub.2 C(CH.sub.2 OSiR.sub.3).sub.3 }.sub.awherein each R, which may be the same or different, is methyl, ethyl or vinyl, at least one R per each --SiR.sub.3 group being methyl, and further wherein a is 1, 2, 3 or 4.