The subject invention provides a viscoelastic polyurethane foam being flame retardant and having a density of greater than two and a half pounds per cubic foot that comprises a reaction product of an isocyanate component, an isocyanate-reactive blend, and a chain extender. The isocyanate-reactive blend includes a first isocyanate-reactive component and a second isocyanate-reactive component. The first isocyanate-reactive component includes at least 60 parts by weight of ethylene oxide (EO) based on 100 parts by weight of the first isocyanate-reactive component and the second isocyanate-reactive component includes at most 30 parts by weight of EO based on 100 parts by weight of the second isocyanate-reactive component. The chain extender is reactive with the isocyanate component and has a backbone chain with from two to eight carbon atoms and is present in an amount of from 5 to 50 parts by weight based on 100 parts by weight of the foam. A composition useful in making the viscoelastic polyurethane foam is also disclosed.