Attic Stair Cover Insulating and Magnetically Sealing Your Pull-down Stairs The Thermalid II magnetically seals the Attic Pull-down Stairway The Thermalid II is seals just like your Refigerator door The Thermalid II provides an R-9 rating with its 2 1/4" thick material. The Thermalid II Inside Measurements 56"L x 28"W x 8.875"H The Thermalid II is professionally designed with the highest grade material.