Plastic Foams for Concrete HomesPortland Cement Association Residential Technology Brief

Many of the benefits of concrete homes built with insulating concrete forms (ICFs) come from the plastic foams of which ICFs are made. Plastic foams are lightweight, easily cut, excellent insulators, and good barriers to air and moisture. They also are strong enough to hold concrete and serve as a backer for interior and exterior finishes.

The ICFs sold in North America are either made of expanded polystyrene (EPS), extruded polystyrene (XPS), polyurethane, or a cement-foam composite. By way of a variety of manufacturing methods and formulations, rigid foam insulation typically is produced by introducing a blowing agent into the manufacturing process creating uniform air pockets throughout. This results in a lightweight foam material with superior thermal properties.

EPS and XPS, while made from the same plastic, differ in manufacturing technique. EPS is a closed-cell foam made by an expansion process incorporating steam within a customized mold cavity. This produces unique shapes based upon the mold design. In this process, EPS can be molded into a variety of densities to meet specific ICF requirements. XPS is closed-cell foam that uses an extrusion process creating a continuous “sheet” of foam that is produced in distinct densities and thicknesses.

Polyurethane foam results when two separate ingredients, an isocyanurate and a polyol, are mixed and react with one another. Cement-foam composites are a mixture of portland cement and individual EPS beads that have been partially expanded.

Most ICF manufacturers select the foam material best suited to their proprietary form system based on performance properties and manufacturing efficiencies desired. But in several ICF systems, the formwork is assembled from standard flat sheets of foam, available from building suppliers. With these systems, the buyer also may have a choice of different types of foam.