as emulsifier it is possible to use anionic cationic and nonionic surfactants suitable anionic surfactants are diphenylene oxide sulfonates alkanesulfonates and alkylbenzenesulfonates alkylnaphthalenesulfonates olefin sulfonates alkyl ether sulfonates alkyl sulfates alkyl ether sulfates alpha sulfo fatty acid esters acylaminoalkanesulfonates acylisethionates alkyl ether carboxylates n acylsarcosinates alkyl phosphates and alkyl ether phosphates as nonionic surfactants it is possible to use alkylphenol polyglycol ethers fatty alcohol polyglycol ethers fatty acid polyglycol ethers fatty acid alkanolamides eo po block copolymers amine oxides glyceryl esters of fatty acids sorbitan esters and alkylpolyglucosides cationic surfactants used are alkyltriammonium salts alkylbenzyldimethylammonium salts and alkylpyridinium salts the emulsifiers are preferably added in amounts of from 0 1 to 5 by weight based on the resin the mixture to be foamed may further comprise customary additives such as pigments and fillers the process is advantageously carried out in a plurality of steps which follow one another directly a alkali metal silicate solution blowing agent and emulsifier are firstly mixed b the alkali metal aluminate solution is added to this mixture the temperature during the addition should be below 50 u00b0 c preferably below 30 u00b0 c and in particular in the range from 10 to 25 u00b0 c at these temperatures the reaction of the silicate with the aluminate commences but a homogeneous mixture can still be produced c the mixture is subsequently heated to above 50 u00b0 c preferably to 80 u2013 100 u00b0 c this results in vaporization of the.