Abstract: Extruded foam boards produced using halogen-free blowing agents from a styrene polymer thermoplastic matrix having a Vicat softening temperature VST B 50 of at most 100.degree. and a melt index MVI 200/5 of at least 5 ml/10 min are at least 20 mm, preferably more than 50 mm and in particular from 80 to 200 mm, thick. Preferred blowing agents for producing the foam boards are carbon dioxide alone, as well as mixtures of carbon dioxide and ethanol and/or dimethyl ether.

Abstract: Process for the production of foam boards having a minimum thickness of 20 mm and a cross-sectional area of at least 50 cm.sup.2 by extruding a mixture of the styrene polymer, from 1 to 10% by weight, based on the styrene polymer, of a blowing agent, wherein the blowing agent contains at least one ether from the group consisting of dimethyl ether, methyl ethyl ether and methyl vinyl ether.

Abstract: A composite foam of low thermal conductivity comprisesa) 20-80% by volume of silica aerogel particles having a mean diameter of from 0.1 to 20 mm and a density of from 0.08 to 0.40 g/cm.sup.3,b) 20-80% by volume of a styrene polymer foam which surrounds the particles of component a) and binds them to one another and has a density of from 0.01 to 0.15 g/cm.sup.3, and, if desired,c) conventional additives in effective amounts.

Abstract: A composite foam of low thermal conductivity comprisesa) 20-80% by volume of silica aerogel particles having a mean diameter of from 0.1 to 20 mm and a density of from 0.08 to 0.40 g/cm.sup.3,b) 20-80% by volume of styrene polymer foam which surrounds the particles of component a) and binds them to one another and has a density of from 0.01 to 0.15 g/cm.sup.3, and, if desired,c) conventional additives in effective amounts.

Abstract: A thermal insulating material based on a pigment-containing silica aerogel is obtainable bya) reacting an aqueous dispersion of sodium silicate and a pigment with a strong acid or sodium silicate with a pigment-containing strong acid to give a pigment-containing silica hydrogen, the pigment being such that it scatters, absorbs or reflects infrared radiation of wavelength 3-10 .mu.m,b) substantially freeing the resulting pigment-containing silica hydrogel from ionic constituents by washing with water,c) displacing the water in the hydrogen by a low-boiling liquid which is inert toward the pigment-containing silica gel,d) heating the liquid-containing silica gel thus obtained under supercritical conditions while completely covered with the liquid, ande) subsequently removing the liquid from the solid by flash vaporization at supercritical temperature.