Composite EPS Insulation Nailbase for Roofs InsulLam™ is an engineered insulation consisting of a closed-cell, lightweight and resilient expanded polystyrene (EPS) bonded to an APA/TECO-rated oriented strand board (OSB) or plywood. The InsulLam foam core is cut from the same high-quality EPS as our InsulRoof roof insulations and, upon request, will meet or exceed the requirements of ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. The OSB is available in nominal thicknesses of 7/16” and 5/8”. The plywood is available in a nominal thickness of 5/8”. InsulLam has excellent dimensional stability, compressive strength and water resistance properties. InsulLam can also be manufactured with an assortment of other cover boards.