There are four basic window frame materials:

Wood

Vinyl/PVC/uPVC

Aluminium

Fiberglass

Each of them has some advantages and some disadvantages and this is exactly what the point of this article is - to determine which frame is most suitable for you and your needs.

Thermal resistance

Considering thermal resistance is probably the most important aspect of a window, we will start with it. Wood and PVC provide the best thermal resistance, Fiberglass is not far off, while Aluminium frames are traditionally notorious for their poor thermal resistance. This is somewhat misleading, because the contemporary aluminium window frames are separated by a thermal break made of a non-conducting substance. This vastly increases thermal resistance, while keeping almost all of the structural sturdiness.

Durability

While somewhat poor in the thermal resistance, Aluminium is by far the most durable of all materials. Fiberglass and vinyl are not as strong as the other materials so they are usually reinforced with other materials such as metal. This gives them solid durability, but it is not as good as aluminium. Wood durability varies as different types of wood offer different durability.

Maintenance

The time and money we will spend on maintenance is very important. There is not much difference between uPVC/PVC, aluminium and fiberglass as they all require very little maintenance - only occasional cleaning and lubrication of hinges is necessary, while wood requires much more than that. Painting will occupy most of your time.

Cost

Cost is as important as any other aspect we analyse, especially if you are on a budget. In this case your choice will most likely be vinyl/PVC or aluminium which are very affordable, although some manufacturers will offer somewhat pricey solutions. Wood and fiberglass cost (much) more.

Recycled content

The recycled content is also very important nowadays and aluminium is the winner here with over 95 %, while fiberglass comes second, wood third and vinyl/PVC and upvc windows and doors last with the least recycled content.

I know I am supposed to come up with a smart solution that would suit most, but I am unable to because we all have different priorities. If you are on a budget, choose PVC, vinyl or upvc, but keep in mind they emit dioxins if they are burned. If you are glazing larger structures, go with aluminium. I would recommend wood only to those that want the most traditional material. The high maintenance, higher cost and the fact it tends to shrink and swell with humidity changes are solid cons.