Firestone ISOGARD HD Cover Board is a half-inch (12.7 mm) thick polyiso insulation designed to prevent heat loss from a building and for use as a cover board. It is a high density, closed-cell, polyisocyanurate foam core that has been manufactured with coated glass facers. Firestone ISOGARD HD Cover Board provides the highest thermal performance when compared to other high density insulations or cover boards. All Firestone polyisocyanurate insulations use EPA accepted blowing agents. Firestone ISOGARD HD Cover Board with ISOGARD foam technology incorporates a HCFC-free blowing agent that does not contribute to the depletion of the ozone layer (ODP-free).