uPVC windows are made from section of frame, which is cut to length and joined together to form the shape of the window. The frames are made by putting molten PVC through a moulding machine and it comes out the other end in long sections of frame which is cooled almost immediately before being cut to length. This makes the frame easy to work with. The window frames are then made into windows and doors that have been cut to the correct size and joined together using heat based welding. Steel or aluminium lengths are then put inside to give it additional strength if required.