Perfect Pet Tubby-Kat Cat DoorUnlike other parts of the world, 90% of companion cats in the United States never go outside. Yet millions of owners have discovered that a cat flap is the ideal way to move the litter pan from the living area of the home to the garage, basement or utility room. And with the litter pan goes the dust, tracking mess, and odor. Also those with dogs and cats can segregate the cat's food and waste from a hungry or curious dog. These have an unbreakable Lexan flap and feature 4 way locks. That means you can set the lock to give free access in or out; in but not out; out but not back in; or completely locked in both directions. The telescoping frame design insures that the core of the door through which you mount it, is covered. This is important as interior doors are often times hollow. Transparent unbreakable Lexan flap with 2-way operation and weatherproof design.