Vinyl vs. Fiberglass Windows: Which One Is Best?

Installing New Construction Window
Installing New Construction Window. DreamPictures/Shannon Faulk/Getty Images

When shopping for new-construction or replacement windows, typically you will be presented with a choice of two materials: vinyl or fiberglass. Both use manmade materials.  Both provide excellent thermal resistance. Both are close to maintenance-free. So which one should you buy?

On a basic structural level, fiberglass windows tend to be superior to vinyl windows. If you are interested in remodeling for the long run or in resale values, fiberglass windows are a clear choice. But with remodeling, decisions rarely come so easily, since a myriad of factors needs to be considered.

One factor is cost. Vinyl windows' lower cost make them a close contender with fiberglass. Another factor is whether or not you can do them yourself. Since new construction vinyl windows are readily available in-stock in major home improvement stores, they can be DIY-installed, saving on labor costs. Fiberglass windows generally are special order items.

Main Points

  • Strength: Fiberglass is stronger than vinyl, with fewer chances of warping.
  • Paintability: Fiberglass framed windows can be painted, unlike vinyl.
  • Eco-Friendliness: Fiberglass windows are considered greener than vinyl because fiberglass windows are about 60% glass, and glass can be recycled.
  • Wood-Look: Fiberglass can mimic the look of wood windows more than vinyl windows can.
  • Resale: Fiberglass is considered more upscale than vinyl windows--better resale value.
  • Cost:  Vinyl will always be cheaper than fiberglass, at least in the foreseeable future. Expect to pay up to 30 percent more for fiberglass than for vinyl.

Materials

For vinyl windows, extruded polyvinyl chloride (PVC) is the base material. Inner structural elements that stiffen the framing may include metal.  

For fiberglass windows, 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.  

Colors and Finishes

Fiberglass does offer more options for color and finish, but not vastly more options. 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 cannot be painted.

Some fiberglass windows, like Milgard's WoodClad series, are constructed with a fiberglass core but have a wood veneer covering the outside (only on the interior side of the window).

Strength

Fiberglass windows can be up to nine times stronger than vinyl windows. One product, Ultrex by Marvin's Infinity Windows brand, makes this claim.

It's important to remember, though, that windows 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.  

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 are in the same arena 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. Fiberglass windows are estimated to have a 38 percent longer lifespan than vinyl, according to a 2007 case study. Also, because fiberglass is sourced from glass--the same material as the window-glass--both frame and window-glass expand and contract at the same rate, leading to less of a chance of seal failure. Seal failure in the IGU, or insulated glass unit, is a major cause of fogging and condensation.

Maintenance

Both windows are equally low maintenance. Mold, mildew, moss, and dirt can be hosed off and then scrubbed with a sponge and warm water.

Insulating Factor

Equal. Because the hollow cavities of both fiberglass and vinyl windows can be filled with insulation, both do a superior job of slowing the transmission of outside temperatures to the inside of the house.

Cost

Vinyl windows are nearly always cheaper than fiberglass windows. Replacement windows are not found on the shelf at home improvement stores, but new construction windows are. Of the new construction windows found at those stores, the only types you will find are vinyl and wood windows. Thus, fiberglass windows currently do not lend themselves to DIY installation.

Glass Space

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 glass space.  

Also, because fiberglass frames are stronger than vinyl, this means that they can contain far larger glass "real estate" than vinyl. In other words, more glass means more natural light. More natural light means lower energy bills in the long term.

Resale Value

Fiberglass windows tend to reap higher resale values than vinyl windows. While windows, in general, are not a large factor in determining the sale price, fiberglass would bring a slightly higher price if considered.