Expanding and contracting uPVC is a natural occurrence. In extreme heat, you may have noticed your windows or doors becoming stiff or not opening or closing properly. This could be because the uPVC has swollen. According to engineeringtoolbox.com, uPVC can expand by up to 2.4cm at 40ºC.
While this seems like quite a lot, your windows and doors aren’t going to suddenly break.
In extreme heat, you can cool down your uPVC by patting it down with a cold, damp cloth or alternatively spraying the outside with water. This should help the uPVC shrink back to size and work freely once more.