Home Depot I got it for cheap . its thin insulation bubble wrap of some kind. doesn't get hot or cold and is vapor proof. whatever hits it bounces off. My heater was left on the other day when I was doing a co2 cycle and my room was 95 degrees when I came home, but when I opened my grow cab, the temp. was only 85 degrees. this feature benefits well in the summer time and prevents the wood of my cabinet from warping