There are various things that can cause PVCu windows to yellow over time but the primary cause is the sun and its UV light. If you have PVCu windows already and they have started to yellow, look at the areas where sunlight is more restricted. They are probably less discoloured there, if at all, than parts of the window frames that are in direct sunlight. If you have a property with south-facing windows, you are likely to have issues with yellowing further down the line.
Aside from the sunlight, the other main cause of yellowing and discolouring to PVCu windows has more to do with the materials used in their construction. The fact that PVCu is recyclable has made it incredibly popular. Particularly as most people are trying to make their lives greener and more environmentally friendly. As a result, though, it means that not all PVCu is made to the same standard. If you opt for a product that has a higher content of plasticising pigments and agents, it could be more prone to turning yellow in the future.
If you are considering replacing your windows or doors, we will happily talk to you about the various options to help you make the right choice.