Using 3/16" polycarbonate and stainless steel hinges, The MagnaFlap Door creates an energy efficient, easy-to-install door designed especially for pets. The tinted polycarbonate reduces reflections and glare, and pre-drilled holes and colored mounting screws streamline installation. The door opens in one direction allowing pets to easily push the door to exit. To reenter, the door has a 55 degree angle on one side. This allows the animal to use their nose to reopen the door by nudging the angled side of the door. Both short and long nosed pets can be trained to use their nose to push the door back open again. The Small and Medium are made with two hinges; the Large doors are made with three to ensure durability, and their stainless steel construction resists rust and corrosion. The MagnaFlap Door is great for kennels, dog runs, dog houses and out buildings.