A quick tutorial on changing a Upvc door panel, thought it might be useful. Most panels are now 28mm thick, but some are 24mm. you can generally use a 28mm one in a door designed for 24mm if using a saw blade you run it 30 - 40 mm deep around the polystyrene in the middle of the panel, this will give you a bit of flexibility when replacing the beads. If your door requires a 28mm panel though, you can't really use a 24mm one.