The most essential part of a pet door is the flap itself. Throughout the history of pet doors, the flap has always been the biggest disappointment to the pet owner. They may leak, not insulate that well, blow open, wear out quickly, or even hurt the pet. Until now! The award winning Endura Flap Pet door for Walls is the premium solution to all of these problems. The Endura Flap is nothing like your current pet door you may have, as you're not going to believe how much better it is! If you get the single flap version, the flap is on the inside of your home (the same side as the locking cover) and if you get the double flap version there is a flap on both sides. The wall mounts come with an 8" thick aluminum tunnel that is self framing for most 2 x4 and 2x6 stud walls.