Attic Stair Cover Insulating and Magnetically Sealing Your Pull-down Stairs Attic Thermalid II magnetically seals the Attic stairs draft free $$$$ Attic Thermalid II provides an R-9 barrier with its 2 1/4" thick cover. Attic Thermalid II open like your Refigerator door Attic Thermalid II install in minutes, easy to open Inside measurements are 56"L x 28"W x 8.878"H.