Abstract: The invention relates to a process for producing heat-insulating material from silicate-containing material, hydrated lime, water, foam and a reactive aluminates-containing quick-setting cement, from which a pourable raw mixture is produced which is poured into molds, the green moldings formed in the molds being demolded and autoclaved after sufficient setting. To achieve very low bulk densities, it is provided that, as silicate-containing material, a quartz powder with a specific surface area according to BET of at least approx. 3 m.sup.2 /g, in particular approx. 4 to 5 m.sup.2 /g, is used, the raw mixture is produced with a weight ratio of water/solids (excluding foam) of at least approx. 1.25 and an essentially stoichiometric amount, with respect to the virtually complete reaction of the quartz powder and the reactive aluminates, of hydrated lime with a surface area according to BET of at least approx. 15 m.sup.