The "STS Pro-Shield Plus Liner" is a 90 mil, Zero Perm, insulating liner with a R-Value of 4+ , Class A Fire rating, 25 Year Warranty, has a 99% pure aluminum foil backing on one side which reflects up to 97% of the heat (which is considered GREEN or energy efficient) and qualifies for the Residential Energy Efficiency Tax Credit. See "TAX CREDIT CERTIFIED" for more info!!! Liner is sold by the roll only, so mix the 50' and 125' roll sizes to get the closest square footage required! Note: Don't forget to add extra for cuts and obstacles. STS Pro-Shield Plus Liner: The liner that does it all! STS Pro-Shield Plus Liner used as the Ultimate Pre-Finish and Carpet Pad for basements: Another great use for our liner is before you finish your basement into your ultimate entertaining spot or recreation room, install the Liner System to walls and floor, before finishing with drywall or paneling and carpeting. This will prevent any moisture from sweating walls or cracks that may appear later, behind your new drywall or paneling, from damaging them with moisture causing MOLD. Sealing the floors prevents any water damage to your new flooring as well. The Liner System will allow the moisture or water that may enter behind and under to flow to the sump pit and be discharged out without causing any damage. There is one more added benefit to adding the liner to the floor, it makes for the Ultimate Carpet Pad.