A surface is insulated by applying an elastomeric foam material. In one embodiment, the elastomeric foam material comprises a polyurethane foam that is formed on-site by reacting an isocyanate with a polyol. In one embodiment, the polyol may include a polyol chain extender and/or a plasticizer. In one embodiment, the elastomeric foam material forms an air barrier against a surface. After the elastomeric foam material is installed, a fibrous insulation material may be then placed over the foam layer.