https://selfless.wiki/wiki/Cat_Flap_Installers
It is possible to put a cat flap in a door panel made of upvc, or a double glazing glass sealed units, although the best option is to purchase a brand new glass pane with an already-made hole. Take note of the instructions that will be included with your cat flap kit and follow them carefully. Make sure that the template sketch accurately depicts the shape (circle or square). Safety A microchip activated pet door in your upvc door is a great solution when you have a pet or cat and would like to let them out in the garden, but don't want to