Process for preparing a polyurethane foam comprising reacting a polyether polyol and a polyisocyanate in the presence of a blowing agent and an antioxidant, wherein: the antioxidant consists of one phenolic antioxidant or two or more phenolic antioxidants, wherein the one or more phenolic antioxidants contain no atoms other than carbon, hydrogen and oxygen, and the amount of the one or more phenolic antioxidants is of from 2,300 to less than 10,000 parts per million by weight (ppmw) based on the polyether polyol; the one phenolic antioxidant or at least one of the phenolic antioxidants is a compound of Formula (II): wherein R 1 is hydrogen or C 1 -C 8 alkyl, n is 1, 2 or 4, X is -CH 2 CH 2 -C(=O)-O- where -CH 2 CH 2 is bonded to the benzene ring and C(=O)-O- is bonded to R 2 , and if n is 1: R 2 is C 1 -C 24 alkyl, or if n is 2: R 2 is C 2 -C 12 alkylene or C 4 -C 12 alkylene interrupted by oxygen, or if n is 4: R 2 is C 4 -C 10 alkanetetrayl; the isocyanate index is of from 110 to 150, preferably of from 110 to 140, more preferably of from 110 to 130, most preferably of from 110 to 125; in a case where the blowing agent comprises water, water is used in an amount of at least 4 parts per hundred parts by weight of polyol (pphp); the maximum temperature during the preparation of the polyurethane foam is higher than 140 °C, preferably of from 150 to 190 °C, more preferably of from 160 to 190 °C; and the density of the polyurethane foam is at most 23 kg/m 3 , preferably of from 6 to 23 kg/m 3 , more preferably of from 10 to 23 kg/m 3 , more preferably of from 12 to 22 kg/m 3 , more preferably of from 13 to 20 kg/m 3 , most preferably of from 14 to 18 kg/m 3 . the antioxidant consists of one phenolic antioxidant or two or more phenolic antioxidants, wherein the one or more phenolic antioxidants contain no atoms other than carbon, hydrogen and oxygen, and the amount of the one or more phenolic antioxidants is of from 2,300 to less than 10,000 parts per million by weight (ppmw) based on the polyether polyol; the one phenolic antioxidant or at least one of the phenolic antioxidants is a compound of Formula (II): wherein R 1 is hydrogen or C 1 -C 8 alkyl, n is 1, 2 or 4, X is -CH 2 CH 2 -C(=O)-O- where -CH 2 CH 2 is bonded to the benzene ring and C(=O)-O- is bonded to R 2 , and if n is 1: R 2 is C 1 -C 24 alkyl, or R 1 is hydrogen or C 1 -C 8 alkyl, n is 1, 2 or 4, X is -CH 2 CH 2 -C(=O)-O- where -CH 2 CH 2 is bonded to the benzene ring and C(=O)-O- is bonded to R 2 , and if n is 1: R 2 is C 1 -C 24 alkyl, or if n is 2: R 2 is C 2 -C 12 alkylene or C 4 -C 12 alkylene interrupted by oxygen, or if n is 4: R 2 is C 4 -C 10 alkanetetrayl; the isocyanate index is of from 110 to 150, preferably of from 110 to 140, more preferably of from 110 to 130, most preferably of from 110 to 125; in a case where the blowing agent comprises water, water is used in an amount of at least 4 parts per hundred parts by weight of polyol (pphp); the maximum temperature during the preparation of the polyurethane foam is higher than 140 °C, preferably of from 150 to 190 °C, more preferably of from 160 to 190 °C; and the density of the polyurethane foam is at most 23 kg/m 3 , preferably of from 6 to 23 kg/m 3 , more preferably of from 10 to 23 kg/m 3 , more preferably of from 12 to 22 kg/m 3 , more preferably of from 13 to 20 kg/m 3 , most preferably of from 14 to 18 kg/m 3 . <EOS>