https://phelps-whittaker.thoug....htlanes.net/cat-flap
Cats are fond of looking out of windows, a pastime sometimes referred to as cat TV. It's a form of entertainment that is often instinctive. You can fit glass window inserts that have cat flaps on existing windows or doors. They can also be fitted to double glazing. Easy to fit Cat flaps can be installed in all kinds of glass doors and windows, including single glazing, double glazing, french doors and patio doors, bifold doors and leaded units. They are great for people who don't want to cut into a wall or door