We developed a sturdy Thermolastic (ABS) frame; a see-through poly vinyl flap with patented edges to not warp; a floating sill to insure good closure; and a strong molded ABS lock-out slide to restrict the petmovements when necessary. Then weMade the Original Pet Door 4 sizes for pets up to 120 pounds.Features: Clear vinyl flap with patented edges that won?t warp from use or extreme temperatures. Floating bottom threshold for perfect seal every time. Lock-out slide to keep your Ideal Pet out of mischief when unsupervised. Average install time: 20 minutes.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?.Exact Measurement/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.