https://postheaven.net/iciclet....urkey4/using-upvc-ca
This cat flap that is insulated has a double-flap system and offers a good amount of protection in various climates. It can be fitted in wood, uPVC, glass, and metal doors. A tightly sealed door is vital, especially in colder weather. It prevents warm air from being sucked away and cold air from entering, saving money on energy costs. Wind Resistance By preventing cold air entering your home and keeping warm air in, a cat flap cover will keep it warmer. Most of the best options are insulated and include a magnetic sea