Aluminum vs Fiberglass Windows
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Aluminum vs Fiberglass Windows

Aluminum windows have long been valued for their strength and durability, earning them a favored place in homes, businesses and buildings of all kinds. But fiberglass windows have gained a lot of popularity in recent years too, and there are good reasons to give them serious consideration when it's time to order replacement windows for your home.

Aluminum vs Fiberglass Windows

When comparing various window materials, a wide range of considerations may sway your decision in one direction or another. Some of the most important factors include:


Fiberglass windows are made through a process called pultrusion, which involves polyester resins being pulled through a heated die, and then impregnated into glass strands or mats. The result is a durable, versatile composite material made of glass fibers and plastic.

Aluminum is made via two different processes. There is extruded aluminum, which is made by pressing the heated aluminum into dies, and there is rolled aluminum, which involves creating thin sheets of aluminum using rollers, much like the aluminum used to make soda clans. Of the two, extruded aluminum is by far the stronger material.

In addition to windows that are fully made of aluminum or fiberglass, cladded windows are also an option. Cladded wood windows have a wood core, which is clad with another material—often aluminum or fiberglass. This may offer a best-of- both-worlds appeal depending on which qualities are most important to you.

Aesthetics/curb appeal

Aesthetics are always, to some degree, a matter of personal choice. But both aluminum and fiberglass windows are known for being adaptable to a wide range of architectural styles and aesthetics. Aluminum window frames tend to be very thin, allowing greater glass surface area and giving them a sleek, minimalist look that is especially at home in modern architecture or reclaimed industrial spaces.

Fiberglass windows often have a similar look, but not always. Thanks to its ability to be cut and molded into virtually any style and shape, fiberglass is highly adaptable, and can be made to resemble other materials for a wide range of uses. It can even be imprinted with "grain" to mimic the look of wood window frames.


Durability is one of the chief advantages of both aluminum and fiberglass windows, and both can last 50 years or more. Both materials have a significant advantage over vinyl windows in this regard, both are stable and unlikely to experience warping like some vinyl windows.

In direct comparison, aluminum is stronger than fiberglass. But in practice, the difference isn't usually a significant one. Fiberglass is more than strong enough for the vast majority of residential uses, while aluminum windows are sometimes required for commercial buildings where they are put under greater stress.


Aluminum and fiberglass windows are both noted for being low-maintenance, and there isn't a significant difference between the two when it comes to maintenance requirements. Both are easy to wash with warm water and a soft scrubbing sponge, and minimal cleaning is all it takes to keep both looking like new for many years. The only exception is in coastal environments, where metal windows are prone to corrosion.

Energy Efficiency

Energy efficiency is the category in which the divide between aluminum and fiberglass windows is most apparent. Aluminum, despite its versatility and strength, is one of the least energy efficient window frame materials. Like a lot of metals, aluminum conducts heat easily, which makes it a poor insulator.

Fiberglass, on the other hand, is an excellent insulator—there's a good chance you have fiberglass insulation in the walls of your home—which makes it highly energy efficient. In fact, the high thermal performance of fiberglass windows makes them among the most energy efficient replacement window options you can get.


Aluminum and fiberglass windows are both more expensive than vinyl windows (and less expensive than wood windows). Comparatively, aluminum tends to be cheaper than fiberglass, but not overwhelmingly so. Both are a good value because of their longevity, but the difference in efficiency can tip the value scales in favor of fiberglass, especially in very hot or very cold climates.


Aluminum windows have been available longer, and are still more widely available than fiberglass windows. But fiberglass windows have gained popularity in the last 20 years, and are now being offered by a wider range of window manufacturers:

  • Milgard - Aluminum windows
  • Marvin Windows - Fiberglass windows
  • Andersen Windows and Doors - Aluminum clad windows and fiberglass clad windows.

Pros and Cons of Aluminum Windows

  • Very strong and durable
  • Ideal for modern and industrial architecture
  • Low maintenance
  • Doesn't warp or swell
  • Slim frames allow greater glass area
  • Not very energy efficient
  • Prone to condensation

Pros and Cons of Fiberglass Windows

  • Excellent energy efficiency
  • Strength and durability
  • Can be made in a wide range of shapes, sizes and styles
  • Low maintenance
  • Doesn't warp or swell
  • Somewhat more expensive
  • Not as widely available

Aluminum and fiberglass are two window materials that offer similar advantages when it comes to strength, minimal maintenance requirements, and curb appeal. But Aluminum gains an edge in terms of upfront cost, while fiberglass excels when it comes to energy efficiency.

If you're still not sure which replacement windows are best for your home, contact us today to learn more about your options.

July 28, 2021
July 20, 2022


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