A viscoelastic polyurethane foam is the reaction product of at least one natural oil derived polyol and at least one aromatic compound having an average of more than one isocyanate group. A viscoelastic polyurethane foam has an air flow of at least about 0.5 l/s, wherein the foam is formed in the substantial absence of copolymer polyol and has not (yet) been mechanically reticulated and is preferably prepared using at least one natural oil derived polyol, more preferably in an amount of at least about 20 weight percent of the polyols used. A process of preparing a viscoelastic foam, comprises steps of (A) forming a reaction mixture including at least one polyol, at least one polyisocyanate, water, at least one catalyst wherein a the polyol comprises at least one natural oil derived polyol; and (B) subjecting the reaction mixture to conditions sufficient to result in the reaction mixture to expand and cure to form a viscoelastic polyurethane foam. In another embodiment, a process comprises steps of (a) forming a natural oil derived polyol composition comprising at least one natural oil derived polyol and water; (b) admixing at least one gelling catalyst and at least one blowing catalyst with the natural oil derived polyol composition to form a catalyst polyol admixture; (c) supplying an isocyanate in an amount corresponding to an isocyanate index for a pMDI of at least about 65 and at most about 95 or, when the isocyanate is a TDI or MDI or combination thereof, at least about 80 and at most about 105; and (c) admixing the isocyanate with the catalyst polyol admixture.