A process for producing an ammonia-treated hydrophilic thermal insulation molding which includes treating a thermal insulation molding containing hydrophilic silica with ammonia by introducing the thermal insulation molding into a chamber and supplying gaseous ammonia until a pressure difference p of 20 mbar is achieved. A process for producing a thermal insulation molding containing hydrophobic silica which includes treating the ammonia-treated hydrophilic thermal insulation molding with an organosilicon compound.