uPVC, like almost all other window frame materials, must be protected from UV radiation or else it will yellow and degrade. Most uPVC frames are covered with a thin coating of paint or foil. And this allows a wide selection of colors. For a more natural appearance, uPVC frames may even have a layer of wood on the inside. Just as with Alu-wood framed windows, in the last few year, more uPVC frames have been offered with an aluminum cover for UV protection and durability. A side benefit of this is that the aluminum can be attached to the uPVC in a way that provides additional strength.