TERRAFOAM HS is a high compressive strength board with unusual physical properties. It is inert closed cell expanded polystyrene (E.P.S.) insulation, with excellent resistance to freeze/thaw, zero capillarity and low moisture absorption. TERRAFOAM HS is a "green" alternative to extruded polystyrene, as it uses no chemical gases that might contrite to global warming or attack the earth's ozone layer. HS will never rot, support mold or mildew and insulating properties do not degrade over time. It's compressive strength is minimum 276 kPa (40 psi).

The thermal resistance of TERRAFOAM HS is permanent! R-Value drift will occur with some insulation products because the insulating blowing gases (HCFCs) will eventually escape. Since EPS contains ordinary air, R-Value will remain the same, indefinitely. TERRAFOAM HS is also more effective at lower temperatures. The R-Value increases as temperatures decrease.