Fiberglass vs. Vinyl Windows Buying Guide

Installing New Construction Window
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When shopping for new-construction or for replacement windows, you have a choice of several different materials in the window frames. Wood windows are still available, but windows framed with aluminum, vinyl, fiberglass (or fiberglass composite) are also available.

Increasingly, the choice comes down to vinyl or some variation of fiberglass or fiberglass composite. How do these materials compare when used for window frames and which one is better overall?

Vinyl Windows

Vinyl windows are made from extruded polyvinyl chloride (PVC) as the base material. They may include metal as an internal structural element to stiffen the frames.

Vinyl windows first appeared in meaningful numbers in the 1970s when small window fabricators began offering vinyl-framed windows to meet custom sizes that large window manufacturers could not offer. It was not until the 1990s, though, that vinyl windows truly became a popular option. Large companies quickly saw the merit in producing vinyl windows. Today, hundreds of major window manufacturers offer full lines of vinyl-framed windows.

The main advantage of vinyl-framed windows is that they are affordable, costing only about half of wood-framed windows, on average. Vinyl windows, too, are energy efficient since they are fabricated using a honeycomb structure that traps air to improve R-value. Vinyl windows can be fabricated to fit any opening size.

Vinyl windows never need to be painted. This advantage can be a parallel disadvantage, though, if you want to paint your vinyl windows. Vinyl windows can be painted, but not effectively as the paint will soon peel away.

Vinyl windows are only available in a limited range of colors.

What We Like
  • Lower cost

  • Easily available

  • Painting not needed

What We Don't Like
  • Weaker structure than fiberglass

  • Few colors available

  • Cannot be painted

Fiberglass Windows

Where vinyl windows succeeded in building a customer base that did not exist before, fiberglass frame windows took it to the next step.

Fiberglass is created when polyester resins are activated by a catalyst and then pultruded, or pulled, through a heated die. Strands of glass or glass mats are impregnated with resins. The finished product is called a lineal and it is machinable and can be shaped. Fiberglass has long been used to create ultra-strong, lightweight materials for skis, surfboards, and canoes. 

Fiberglass (and fiberglass-composite windows) began to gain popularity around 2000. They were originally developed to address certain limitations to vinyl windows.

During vinyl's lifespan, it progressively loses its resiliency—a drawback that fiberglass does not have. Fiberglass is also stronger than vinyl. Fiberglass windows also can accomplish the same level of energy-efficiency with smaller frames with a lower profile, making fiberglass frames a more attractive option. And fiberglass can be fabricated in a manner that closely resembles wood—right down to being able to paint it different colors.

Recent fiberglass windows are more accurately described as fiberglass composites since they are fabricated with a mixture of fiberglass and polyester resins. Stronger than wood and occupying a price range between vinyl and wood, fiberglass-framed windows are an increasingly popular choice.

What We Like
  • Strong construction

  • Textured surfaces available

  • Many colors

What We Don't Like
  • Higher cost

  • Do-it-yourself installation difficult

Cost

Both vinyl and fiberglass windows are cheaper than wood, but of the two, vinyl is the less expensive alternative. Vinyl windows are roughly 10- to 30-percent cheaper to buy and install. The cost of installing a single vinyl window $700 to $800, compared to $900 to $1,100 for one fiberglass window.

When cost is the sole determiner for purchase, vinyl windows clearly and consistently win out over fiberglass windows.

Do-It-Yourself Installation

Vinyl windows have a definite advantage, as they are fairly easy for do-it-yourselfers to source and to install by themselves. Fiberglass windows, on the other hand, must be installed with great precision because the material is very rigid, requiring close tolerances.

Professional installation is best with any type of new-construction or replacement window. But with fiberglass windows, professional installation is virtually mandatory. Some fiberglass window manufacturers may be reluctant to sell windows directly to homeowners, and may not warrant them if they are not installed by approved contractors.

Vinyl windows are often stocked at home improvement centers for easy purchase, while fiberglass windows must be special ordered.

Strength and Durability

Vinyl and fiberglass windows are both made from inert substances that do not rot and are not tempting to insects like termites or carpenter ants. In that sense, vinyl and fiberglass windows rank close together for durability, especially when compared to wood windows—made from organic materials that bugs love to eat and which can rot.

Between vinyl and fiberglass, fiberglass windows will be more durable structurally. Fiberglass windows are estimated to have a 38-percent longer lifespan than vinyl, according to a 2007 study.

Also, because fiberglass is sourced from glass—the same material as the window-glass—both frames and glass panes expand and contract at the same rate, leading to less chance of seal failure. Seal failure in the IGU (insulated glass unit) is a major cause of fogging and condensation. Vinyl windows have welded corner seams, which is where seal failure usually occurs.

Fiberglass makes for a stronger, more rigid frame than either vinyl or wood. These windows do not warp, ever. They are very low maintenance—other than painting them if you so choose. Fiberglass can be as much as nine times stronger than vinyl.

It's important to remember, though, that windows themselves provide no structural support. So the sheer ability to support heavy weights (an advertising claim of some fiberglass window manufacturers) is helpful, but not as meaningful as it seems on the surface. If the window opening is framed properly, vinyl windows do perform well. 

Maintenance

Both windows are equally low maintenance. Mold, mildew, moss, and dirt can be hosed off and then the frames cleaned by scrubbing with a sponge and warm water.

Environment

Fiberglass gets the nod here, mostly because the fiberglass used in the window frames consists of about 60-percent recycled glass. Vinyl windows are made from PVC plastic, a material that is difficult to recycle at the end of its life.

Appearance

Fiberglass windows provide more glass space than vinyl windows. Since vinyl is not as strong as fiberglass, more material is needed for the frames. This means that vinyl window frames are slightly thicker than fiberglass, impinging on valuable glass space. Fiberglass windows contain more glass space than vinyl—and more glass means more natural light.

Fiberglass can also be textured to closely resemble the texture of natural wood. Fiberglass windows come in a wide range of colors not found with vinyl windows. Vinyl windows come in a number of baked-in colors, as do fiberglass windows. But fiberglass has the additional advantage of being paintable, while vinyl windows are difficult to paint and maintain over the long-term.

Some fiberglass windows are constructed with a fiberglass core and a wood veneer covering the outside (only on the interior side of the window).

Energy Efficiency

The glass fibers in fiberglass do not expand and contract under heat and cold, and thus they are a slightly better insulator than vinyl. Fiberglass is rated as roughly 15-percent higher in R-value than vinyl-framed windows. Both types, however, offer very good insulating value, since they are constructed with hollow cavities that do a good job of slowing the transmission of thermal energy.

Along with better energy efficiency, fiberglass windows are better at providing insulation from noise transmission.

Real Estate Value

Fiberglass windows tend to reap higher resale values than vinyl windows. In general, windows are not a large factor in determining the sale price of a home, unless they are in extremely poor condition. But between fiberglass and vinyl windows, fiberglass windows would command a higher resale price if the buyer were to consider windows.

Deciding Factors

Both vinyl-framed and fiberglass-framed windows are good products that may be a better choice than wood when it comes time to choose new-construction or replacement windows.

Vinyl has the advantage when cost is the main factor. They work well for inexpensive home remodels and for house flips. For the best appearance and strength, fiberglass windows are the preferred option.