https://selfless.wiki/wiki/Fitting_a_Cat_Flap
This double-flap, insulated cat flap is a great protection for all climates. It can be fitted in wood, uPVC, glass, and metal doors. It is essential to have a door that is sealed tightly, especially during cold winter months. It prevents warm air from getting sucked out and cold air getting in and causing you to pay more energy costs. Wind Resistance By blocking cold air from entering your home and allowing warm air in, a cat flap cover keeps it warm. are those that have a magnet seal and are lined with insulation. They also have a lock to