To choose a high-quality plastic window, you should carefully study the manufacturers that produce metal-plastic windows. You also need to make sure that the certificate of conformity, the certificate of din ven is 9001, license for the production of building structures and the most important thing, this is a license for installation (installation) of structures. You should take an interest in the guarantee of the parts of the metal -plastic window and agree with the contractor so that its obligation includes eliminating the seizures of structures and installation immediately after its installation, if such problems suddenly arise. Naturally, you need to study the prices for plastic windows, because the most expensive product is far from always the highest quality.