Heavy-duty, one piece craft board frame. Double Strut design for performance and durability. 10% greater open area compared to other furnace filters. Easy to install and remove. No metal parts or sharp edges. Provides good equipment protection. Glasfloss GDS 24x24x1 disposable, double-strut furnace filters are excellent for protecting your heating and cooling system and indoor air. These air filters offer a double-strut design that provides durability and a 10% greater open surface area than traditional fiberglass filters. The air filter frame is constructed of heavy-duty craft board that the fiberglass media is bonded to.