All doors, regardless of the materials, will expand to a greater or lesser degree during the heat of the summer. The issue is really how much this happens, and how this impacts the door fitting.
We chose Rockdoor as our composite door supplier, as they have put extensive research into their products. They offer a ‘no-bow guarantee’ on all their doors, so you can buy with confidence knowing that your door will remain properly in place, no matter how hot it gets.