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It is possible to insert a cat flap into the upvc panel, or even a double glazing sealed unit. The best solution is to put in an entirely new glass pane that has a hole that is already made. Follow the directions that should be included with your cat flap kit and follow them carefully. Ensure that the shape drawn (be it circle or square) is accurately drawn on your template drawing. Safety If you have a cat or dog and want to let them in the garden without opening the door, a microchip-activated pet flap i