The physical blowing agents may be included in the foam formulation to reduce the foam density. These agents can be used in addition to, or as partial replacement for, the chemical blowing agent in developing special foam properties. An example is the use of HCFCs, cyclopentane or methylene chloride in formulated polyols for improving the resulting foam. Another important effect of adding physical blowing agents to the formulation is to reduce the rate and amount of heat buildup in polyurethane foams form.
