The lightweight strength and excellent insulating potential of rigid urethane foam have been applied to concrete construction as a means of further extending its economy and performance. One important characteristic which rigid urethane foam shares with concrete is its plasticity and consequent versatility in forming. Rigid urethane foam is available in preformed panels that can be used as delivered or cut to the desired shape. On the other hand, portable foam mixing equipment is available to inject the flowable foam in to cavities where it will soon harden and thereby add the strength and insulating properties of the member. Rigid urethane foams for insulating are often used on roofs, around pipes, between masonry and plaster, for sandwich panel cores, and in other applications involving lightness of weight with high insulation value and a small amount of strength. A 1963, Iowa State Highway Commission study may have discovered another application of urethane foam. The commission to study was to determine if an insulating material could prevent freezing of the subgrade. If so, the need to replace poor soils with granular material would be eliminated. Representative insulated concrete slabs were put through a severe winter and the results should that the foamed plastic insulation beneath the slab adequately protected the subgrade form freezing temperatures, thereby preventing frost heave. The presence of the insulating layer did cause the slab to experience more freeze thaw cycles than if the layer hadn't been there, but engineers haven't yet decided whether this is detrimental.