Thermal Shield (25 ft x 3.5 ft) is a silver and white poly-mylar infused with metals that give protection from outside intrusive sources. Temperature, Vapor, and Thermal barriers are created when using Thermal Shield and the poly-mylar has an extremely high reflective index. This is a absolute must to seal your Grow Room and insure peace of mind!! Available in 25, 50, and 100 ft rolls.