Building codes and many architectural specifications require polystyrene foam building thermal insulation boards to comply with the requirements of ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, published by ASTM International (more info here). ASTM C578 covers the types of foam insulation and the required physical properties of polystyrene foam insulation boards made by extrusion (XPS) or molding (EPS) of expandable polystyrene.
ASTM C578 includes a table of physical property requirements for several Types of XPS (and EPS) foam insulation boards. For example, Type IV XPS is required to demonstrate a minimum compressive strength of 25 psi, whereas Type VII XPS requires a minimum 60 psi compressive strength. The table below is recreated, in part, to show only XPS information listed in the more complete table of ASTM C 578. ASTM C578 is a copyrighted document, so please obtain the actual standard from ASTM for more complete information pertaining to this table and the test methods required to be used to evaluate performance.
* ASTM C 578 also classifies molded expanded polystyrene foam (EPS) material in “Types” not listed here. EPS is made with a different manufacturing process and is sometimes referred to as beadboard. Please refer to the standard for EPS-related performance.
** ASTM E 84, Standard Test Method for Surface Burning Characteristics of Building Materials, describes how flame spread and smoke development properties are tested. Building codes include mandatory requirements for flame spread and / or smoke development for XPS (and EPS) foam insulation. We have inserted the common maximum allowable values in this table because this information is so commonly requested.