Abstract: A heat-insulating material comprising from 85 to 98 parts by weight of mineral wool and from 15 to 2 parts by weight of a binder applied onto the wool, which is a modified resol phenol-formaldehyde resin on the basis of phenol, formaldehyde, sodium hydroxide, a water proofing additive which is an individual alkylresorcinol with a number of side chain carbons of 2 to 8 or a mixture of alkylresorcinols, as well as urea, or dicyandiamide, or melamine, the ratio between said components being as follows (parts by weight):______________________________________ phenol 1 formaldehyde 0.74-0.96 sodium hydroxide 0.03-0.05 alkylresorcinol with a number of side chain carbons of 2 to 8, or a mixture of alkylresorcinols 0.075-0.45 urea, or dicyandimaide, or melamine 0.15-0.35 ______________________________________The proposed heat-insulating material features improved adhesion properties, has a reduced water absorption and an increased moisture resistance.