from about 400 to 10 000 which have at least two hydrogen atoms capable of reacting with isocyanates surface active additives such as emulsifiers and foam stabilizers may also be used according to the invention suitable emulsifiers include e g the sodium salts of ricinoleic sulphone or salts of fatty acids with amines such as oleic acid diethylamine or stearic acid diethanolamine alkali metal or ammonium salts of sulphonic acids such as dodecylbenzenesulphonic acid or dinaphthylmethane disulphonic acid or of fatty acids such as ricinoleic acid or of polymeric fatty acids may also be used as surface active additives suitable foam stabilizers are particularly the polyether siloxanes and especially those which are water soluble these compounds generally have a polydimethylsiloxane group attached to a copolymer of ethylene oxide and propylene oxide foam stabilizers of this kind have been described for example in u s pat nos 2 834 748 2 917 480 and 3 629 308 other additives which may also be used according to the invention include reaction retarders e g substances which are acid in reaction such as hydrochloric acid or organic acid halides cell regulators known per se such as paraffins or fatty alcohols or dimethyl polysiloxanes pigments dyes flame retarding agents known per se such as tris chloroethylphosphate tricresyl phosphate or ammonium phosphate and polyphosphate stabilizers against ageing and weathering plasticizers fungistatic and bacteriostatic substances and fillers such as barium sulphate kieselguhr carbon black or whiting other examples of surface active additives foam stabilizers cell regulators reaction retarders stabilizers flame retarding substances plasticizers dyes fillers and fungistatic and bacteriostatic substances which may be used according.