A process for producing viscoelastic flexible polyurethane foams having an air flow value of at least 1 dm 3 /s, which comprises a) polyisocyanate being mixed with b) polymeric compounds having isocyanatereactive groups, c) optionally chain-extending and/or crosslinking agents, d) optionally compounds having one isocyanatereactive group with a hydroxyl number of 100 to 500 mg KOH/g, e) catalyst, f) blowing agent, and also optionally g) addition agents to form a reaction mixture and convert it into flexible polyurethane foam, wherein the polymeric compounds having isocyanatereactive groups (b) comprise bl) 10 to 40 wt% of at least one polyalkylene oxide having a hydroxyl number of 90 to 300 mg KOH/g, based on a 3 to 6-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, b2) 5 to 20 wt% of at least one polyalkylene oxide having a hydroxyl number of 10 to 60 mg KOH/g, based on a 2 to 4-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, b3) 10 to 50 wt% of at least one polyalkylene oxide having a hydroxyl number of 10 to 55 mg KOH/g, based on a 2 to 4-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 70 to 100 wt%, and b4) 0 to 20 wt% of at least one polyalkylene oxide having a hydroxyl number of 50 to 200 mg KOH/g, based on a 2-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, and wherein the fraction of compounds b1) to b4), based on the total weight of polymeric compounds having isocyanate-reactive groups (b), is at least 80 wt%. a) polyisocyanate being mixed with b) polymeric compounds having isocyanatereactive groups, c) optionally chain-extending and/or crosslinking agents, d) optionally compounds having one isocyanatereactive group with a hydroxyl number of 100 to 500 mg KOH/g, e) catalyst, f) blowing agent, and also optionally g) addition agents to form a reaction mixture and convert it into flexible polyurethane foam, wherein the polymeric compounds having isocyanatereactive groups (b) comprise bl) 10 to 40 wt% of at least one polyalkylene oxide having a hydroxyl number of 90 to 300 mg KOH/g, based on a 3 to 6-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, b2) 5 to 20 wt% of at least one polyalkylene oxide having a hydroxyl number of 10 to 60 mg KOH/g, based on a 2 to 4-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, b3) 10 to 50 wt% of at least one polyalkylene oxide having a hydroxyl number of 10 to 55 mg KOH/g, based on a 2 to 4-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 70 to 100 wt%, and b4) 0 to 20 wt% of at least one polyalkylene oxide having a hydroxyl number of 50 to 200 mg KOH/g, based on a 2-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, and wherein the fraction of compounds b1) to b4), based on the total weight of polymeric compounds having isocyanate-reactive groups (b), is at least 80 wt%. bl) 10 to 40 wt% of at least one polyalkylene oxide having a hydroxyl number of 90 to 300 mg KOH/g, based on a 3 to 6-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, b2) 5 to 20 wt% of at least one polyalkylene oxide having a hydroxyl number of 10 to 60 mg KOH/g, based on a 2 to 4-functional starter molecule and a propylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, b3) 10 to 50 wt% of at least one polyalkylene oxide having a hydroxyl number of 10 to 55 mg KOH/g, based on a 2 to 4-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 70 to 100 wt%, and b4) 0 to 20 wt% of at least one polyalkylene oxide having a hydroxyl number of 50 to 200 mg KOH/g, based on a 2-functional starter molecule and an ethylene oxide fraction, based on the alkylene oxide content, of 80 to 100 wt%, and wherein the fraction of compounds b1) to b4), based on the total weight of polymeric compounds having isocyanate-reactive groups (b), is at least 80 wt%.