The application ex-change core

An inorganic solidified insulating foam material having a rigid structure comprising silicic acid is made by frothing a mixture of aqueous solution of one or both of two certain alkali metal silicates, a surface tension depressant and a silicon dioxide polymer forming agent with or without the inclusion of an alkali metal silicate gelling agent. The foamed material is permitted to harden free of damaging contraction or expansion under conditions of high humidity, approaching 100% relative humidity.