The molecular structure, amount, and reaction temperature of each ingredient determine the characteristics and subsequent use of the foam. Therefore, each formulation must be designed with the proper ingredients to achieve the desired properties of the final material. For instance, a switch in blowing agent may require an increase in this additive to maintain thermal properties. Increasing the amount of blowing agent requires more water and a switch in surfactants to maintain optimum bubble sizes and formation rates during foaming. The density of the foam is determined by the amount of blowing. The stiffness and hardness of polyurethane can also be tailored by changing the level of flexible polyol in the chemical formulation. By mixing different combinations of the starting ingredients may produce different material structure.