There are several reasons for the popularity of PVC frames, but there are also reasons to consider aluminum-framed windows in the home.
Properties
PVC window frames are also called “vinyl” frames, because they are made from rigid, impact-resistant polyvinyl chloride (PVC). They have hollow spaces inside the frames that make them resistant to heat loss and condensation.
Aluminum is a relatively inexpensive metal, it's strong and durable and easily shaped into any length to frame windows.
Cost
One major factor in the popularity of PVC windows is that many cost less than aluminum frames. PVC does come in varying qualities, and some of the best quality PVC is in line with the cost of aluminum.
Security
PVC is not as strong as aluminum, and because of the tight fit possible with aluminum-framed double glazed windows, they are favored for security. It's difficult to pop out a window from an aluminum frame if it has been properly installed. Some of the more expensive PVC frames are reinforced with metal to make them more secure.
Maintenance and Durability
Both aluminum and PVC window frames are easily cleaned with a damp cloth.
Both are also durable, although inexpensive PVC window frames tend to expand and contract when exposed to extremes of heat and cold, making them harder to operate and prone to air leakage. Vinyl window frames cannot be painted and darker shades may fade over time.
Aluminum windows never need painting, don’t rot or warp and are rigid and strong enough to bear the load of window lintels with minimal reinforcement. Over time, however, aluminum can deteriorate in coastal areas with salty air.
Insulation
Another reason that PVC frames are popular is because they are excellent insulators. Thermalcare and other PVC frame manufacturers often quote a study by BRANZ, an independent building research company, that twice as much heat loss occurs with aluminum windows than with PVC. Aluminum conducts heat from the home and dissipates it to colder surroundings. It is possible to buy aluminum frames that have been fitted with a less conductive material between the panes of windows to prevent heat loss.