Use of bonded siloxane block polymers of the average general formula M a M 1 b D c D 1 d T e Q f G g formula with G = independently identical or different radicals from the group of: a = 0-20, preferably 0-10, especially 2.4-4.1, b = 0-20, preferably 0-10, especially 0, c = 3-450, preferably 5-350, especially 10-250, d = 0-40, preferably 1-30, especially 1.5-20, e = 0-20, preferably 0-10, especially 0, f = 0-20, preferably 0-10, especially 0, g = 0.1-3, preferably 0.15-2, especially 0.2-1.5, where a + b ≥ 2 and N = a + b + c + d + e + f + g ≥ 11 and ≤ 500, b + d ≥ 1 R = independently identical or different alkyl radicals having 1-16 carbon atoms or aryl radicals having 6-16 carbon atoms or H or -OR3, preferably methyl, ethyl, phenyl, octyl, dodecyl or H, especially methyl, R 1 = independently identical or different polyether radicals, preferably identical or different polyether radicals of the general formula R 2 = independently identical or different divalent organic radicals, preferably identical or different divalent organic radicals which have 2-30 carbon atoms and are optionally interrupted by ether functions or (-SiR 2 O-) n - groups and optionally bear OH functions, R 3 = independently identical or different alkyl radicals having 1-16 carbon atoms or aryl radicals having 6-16 carbon atoms or H, R 4 = identical or different alkyl radicals which have 1 to 18 carbon atoms and optionally have ether functions, or aryl radicals which have 6-18 carbon atoms and optionally have ether functions, or H, preferably H, ethyl and benzyl, R 5 = identical or different radicals from the group of: R 3, H, -C R 3, preferably methyl, butyl, H or -C Me, n = independently 1 or 2 m = independently 1 or 2 m + n = 3 h = 2-18, preferably 2-10, especially preferably 3, i = 0-100, preferably 0-80, especially preferably 0-50, j = 0-100, preferably 0-80, especially preferably 0-50, k = 0-100, preferably 0-80, especially preferably 0-50, l = 0-80, preferably 0-40, especially preferably 0, with the proviso that i + j + k + 1 ≥ 3, as additive in the production of viscoelastic polyurethane foam using polyol mixtures and at least one isocyanate component, wherein the polyol component used overall has an average hydroxyl number, determined to DIN 53240-1:2012-07, of 57-300 mg KOH/g, and wherein the PUR foam is produced at an isocyanate index of 65 to 108. G = independently identical or different radicals from the group of: a = 0-20, preferably 0-10, especially 2.4-4.1, b = 0-20, preferably 0-10, especially 0, c = 3-450, preferably 5-350, especially 10-250, d = 0-40, preferably 1-30, especially 1.5-20, e = 0-20, preferably 0-10, especially 0, f = 0-20, preferably 0-10, especially 0, g = 0.1-3, preferably 0.15-2, especially 0.2-1.5, where a + b ≥ 2 and N = a + b + c + d + e + f + g ≥ 11 and ≤ 500, b + d ≥ 1 R = independently identical or different alkyl radicals having 1-16 carbon atoms or aryl radicals having 6-16 carbon atoms or H or -OR3, preferably methyl, ethyl, phenyl, octyl, dodecyl or H, especially methyl, R 1 = independently identical or different polyether radicals, preferably identical or different polyether radicals of the general formula R 2 = independently identical or different divalent organic radicals, preferably identical or different divalent organic radicals which have 2-30 carbon atoms and are optionally interrupted by ether functions or (-SiR 2 O-) n - groups and optionally bear OH functions, R 3 = independently identical or different alkyl radicals having 1-16 carbon atoms or aryl radicals having 6-16 carbon atoms or H, R 4 = identical or different alkyl radicals which have 1 to 18 carbon atoms and optionally have ether functions, or aryl radicals which have 6-18 carbon atoms and optionally have ether functions, or H, preferably H, ethyl and benzyl, R 5 = identical or different radicals from the group of: R 3, H, -C R 3, preferably methyl, butyl, H or -C Me, n = independently 1 or 2 m = independently 1 or 2 m + n = 3 h = 2-18, preferably 2-10, especially preferably 3, i = 0-100, preferably 0-80, especially preferably 0-50, j = 0-100, preferably 0-80, especially preferably 0-50, k = 0-100, preferably 0-80, especially preferably 0-50, l = 0-80, preferably 0-40, especially preferably 0, with the proviso that i + j + k + 1 ≥ 3, as additive in the production of viscoelastic polyurethane foam using polyol mixtures and at least one isocyanate component, wherein the polyol component used overall has an average hydroxyl number, determined to DIN 53240-1:2012-07, of 57-300 mg KOH/g, and wherein the PUR foam is produced at an isocyanate index of 65 to 108.