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It is possible to install an apron flap inside a upvc panel or a double glazing sealed unit. However, the best solution is to put in a new glass pane with a pre-made hole. Follow the directions that came with your kit. Make sure the shape you've drawn (be it square or circle) is accurately depicted 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 in your door panel made of upvc is a great choice. This