I built a cage from 3/8" birch plywood. The ambient room temperature is a bit cool in the winter for my california kingsnake, so I placed the heat mat underneath the cage, and it covers about half the cage floor. Though the the manufacturer recommends against placing the mat underneath a wooden cage, it seems to work well; perhaps it wouldn't on thicker wood. This heat mat doesn't have adhesive on the surface, which differs from other brands, but I prefer this arrangement. The cage is set on 2 x 4s edgewise, and the edges of the pad are supported by the 2 x 4s. Using a spacer, or not, you can adjust the proximity of the mat to the bottom surface of the cage--flush against the cage would be warmer and with spacers it would be cooler. I have ordered a dimmer switch to adjust the temperature, but this may not be necessary.I am well pleased with this heat mat, and the shipping time was amazingly quick--2 days with regular shipping!When using a heat mat for reptiles, it's necessary to provide a gradient of heat-cool in the cage so the animal can move about and thermoregulate. In my cage I have a shelf added for two levels. The snake can spend time on the upper level retreat or in the rock cave on the lower, heated level.