So here a lot is being mixed up. 1.) Plastic can become brittle due to temperature/UV, but that does not mean that this is always the case. Furthermore, the "worn" surface does not result from brittleness, but the material is simply stressed and worn by wind (particles), water, chemicals, etc. You can see the same with metals and wood. Glass and paints are somewhat less sensitive, but anyone who looks at the windows and paint of their 20-year-old car will probably notice that they are no longer like new either. 2.) Plastic, glass, and metal have different coefficients of thermal expansion, but this is independent of the color of the window. Dark films CAN increase the surface temperature, but since plastic is a good insulator, this only applies to the near-surface layers. In addition, the plastic on the outside always heats up more than the inside of the house. Furthermore, those who argue with expansions here should take a look at the difference in the coefficients of thermal expansion of glass, plastic, and aluminum. If the few degrees difference caused by a dark film were already a problem, then no window would be tight anymore and the panes would fall out everywhere. 3.) Sure, some plastic windows no longer look like new. But as already mentioned, these have only been standard for 40 years. Metals and wood have been used for centuries. In the field of plastics, development has progressed enormously since the 1970s, while the other material sectors have only developed slightly. This means: Even if they are still white, plastic windows from the 1980s are not comparable to the current standard.