Whether you live and work in the Great Plains or North where the temperature plummets, or in the South-east or West where Summer is endless, the cost of energy has sky rocketed. So, either heating or cooling the back yard with an old fashioned dog door just won't do anymore. In some cases the energy waste is like opening and closing the door itself 4 or 5 times a day.Ideal Pet has the answer with The Ruff-Weather Door's air pocket between 2 soft flaps, makingit great energy efficient insulator.The Ruff-Weather series in Small, Medium, Extra Large and Super Large are designed to give an air pocket of up to 3 inches between the 2 flaps in a dog door installation. And with the available wall tunnel kit, an air pocket of up to 9 inches. This is serious energy efficiency.Features: Energy efficient structural foam molded plastic. Tamper Proof Mounting System, pet door can't be removed from outside. Nylon for draft restrictor. Innovative Double Vinyl Flap design creates energy efficient air pocket for maximum insulation. Optional pet door Wall Kit, sold separately, item ID: RWXLWK.Door Sizes And Pet Weight: If your cat is smaller than about 15Lbs or your dog is smaller than about 8 Lbs, a flap size of around 5" x 7". If 8 Lbs and 35 Lbs consider a flap size around 8" x 11". If your dog is between 35 Lbs and 80 Lbs consider a flap size around 10" x 15. If your dog is over 80 Lbs consider a flap size of 15 x 20?.Measure your petwidth: Simply open a door the minimum width needed for the widest part of your pet to comfortably walk through, then measure the door opening and add an inch. You can also stand above your pet and use a ruler to measure the widest portion of your pet, then add an inch.its important to add an inch or so, that way your pet will not rub on the door as they pass through. Determine your petheight by measuring from the top of your dog shoulders toits belly or chest and add 2 inches.