The "STS 22mil Liner" is sold by the roll, each roll is 12'x50' = 600sq ft. The liner is a Nylon Reinforced Flexible Polyethylene Plastic Sheeting. This is an excellent second option to the STS Pro Shield 90mil Liner for encapsulating a crawl space. The 22mil Liner seals out most gasses, odors & moisture even though it is not Zero Perm. It has an Antimicrobial coating that won't support Mold growth and still has the 25yr manufacture warranty. Note: Don't forget to add extra for cuts and obstacles when measuring.