Expanded Polystyrene Board Insulation

Expanded polystyrene (EPS) is a rigid polystyrene foam board with a more open structure that is more permeable to humidity than extruded polystyrene. If you break a piece of EPS, you see its characteristic structure of little beads of foam all stuck together.

For insulation in contact with the ground, such as under slabs and exterior foundation walls. Look for products with a low global warming potential (GWP), that use carbon dioxide or water as their main blowing agent. You can also ask whether the manufacturer has switched from HBCD flame retardant, a toxic substance that is now being phased out in foam insulation in the European Union and Canada, to less toxic PFR (polymeric flame retardant).

Expanded polystyrene has a high insulation value to save energy, and is one of the few types of insulation that can be used underground, such as under a slab or on the outside of a foundation wall. Unlike extruded polystyrene, expanded typically does not use high global warming potential (GWP) blowing agents, so expanded polystyrene is environmentally preferable to extruded polystyrene. This difference is decreasing as manufacturers of extruded improve their blowing agents.

The first polystyrene was made in 1839 by Eduard Simon in Berlin, of resin distilled from the American sweetgum tree. Today polystyrene is made from petroleum products.