Extruded Polystyrene Board Insulation

Extruded polystyrene (XPS) is a rigid polystyrene foam board with small, closed cells (bubbles). XPS is quite uniform in its internal structure. Polystyrene has a high insulating factor of R4 to R5 per inch.

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).

Extruded 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. However, it is often made using HFCs as a blowing agent (to make the bubbles). HFCs have a high global warming potential (GWP), which means the manufacturing process has a strong negative impact on our climate. Companies are reducing their HFCs and switching to blowing agents like water and carbon dioxide, that have lower GWP.

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.