Foil Vapor BarrierPerforated foil vapor barrier for your sauna. Install with a 6" overlap (start at the bottom of the wall and work your way up). You can get a custom length ($2. 56 per linear foot) or 79' foot standard lengths. To select a custom length, manually adjust the quantity: Qty 1 = 1 foot. Foil is 4 feet wide. Visit https: saunasupplyco. com sauna foil vapor barrier calculator to calculate how much vapor barrier you need for your sauna, or use the table