Everything is simple — you need to keep them clean. Since the plastic is very vulnerable, it must be protected and not subject to various detergents. Therefore, washing the window profile should be carried out by ordinary soap solution and no more, the production of PVC plastic windows this allows. Also, when washing, you need to take care of sealing elastic bands that are responsible for the tightness of the window. If you damage them, then the window can blow out or flow during the rain. Therefore, it will be enough to wipe them with an ordinary damp cloth, and then wipe them dry.