Last reviewed October 27, 2026
Published compressive strength is a test property, not automatically an allowable long-term design stress. Foundations, slabs and heavily loaded assemblies require project-specific engineering using the selected product’s complete data.
An RFQ should identify insulation type, thickness, minimum compressive strength, board size, edge profile, thermal requirement, water exposure, load duration and required documentation.
ASTM C578 classifies rigid cellular polystyrene products, but manufacturer-specific high-load products still require a current data sheet and confirmation of the test basis.
Technical guidance is general. Confirm the selected manufacturer’s current documentation, project drawings, professional design and applicable authority requirements.