FRP Composites Around The House

Person installing fiber glass insulation above a window.
Window Insulation is Full of Fiber Glass.

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Examples of composites can be seen day in and day out, and surprisingly, they can be found all throughout the house. Below are a few examples of composite materials that we come in contact with on a daily basis in our homes.

Bath Tubs and Shower Stalls

If your shower stall or bathtub is not porcelain, chances are good that it is a fiberglass reinforced composite tub. Many fiberglass bathtubs and showers are first gel coated and then reinforced with glass fiber and polyester resin.

Most often, these tubs are manufactured through an open molding process, usually either chopped gun roving or layers of chopped strand mat. More recently, FRP tubs have been manufactured using the RTM process (Resin Transfer Molding), where positive pressure pushes thermoset resin through a ​two-sided hard mold.

Fiberglass Doors

Fiberglass doors are an excellent example of composites. Composite doors have done such an amazing job imitating wood, that many people cannot tell the difference. In fact, many glass fiber doors are made from molds that were originally taken from wood doors.

Fiberglass doors are long-lasting, as they will never warp or twist with moisture. They will never rot, corrode, and have excellent insulative properties.

Composite Decking

Another example of composites is composite lumber. Most composite decking products such as Trex are not FRP composites. The materials working together to make this decking a composite are most often wood flour (sawdust) and thermoplastic (LDPE low-density polyethylene). Frequently, reclaimed sawdust from lumber mills is used and is combined with recycled grocery bags.

There are many advantages of using composite lumber in a decking project, but there are some who would still prefer the sight and smell of real lumber. There is no traditional reinforcing structural fiber such as fiberglass or carbon fiber, however, the wood fiber, although discontinuous provides the structure to the composite decking.

Window Frames

Window frames are another excellent use of FRP composites, most commonly fiberglass. Traditional aluminum window frames have two drawbacks which fiberglass window improve upon.

Aluminum is naturally conductive, and if a window frame is made with an extruded aluminum profile, the heat can be conducted from the inside of the house to the outside, or the other way around. Although coating and filling the aluminum with insulated foam help, fiberglass profiles used as window lines offer improved insulation. Fiberglass reinforced composites are not thermally conductive and this reduces heat loss in the winter, and heat gain in the summer.

The other major advantage of fiberglass window frames is that the coefficient of expansion of both the glass frame and the glass window are almost exactly the same. The pultruded window frames are upwards of 70% glass fiber. With both the window and the frames being primarily glass, the rate at which they expand and contract due to heat and cold is almost the same.

This is important because aluminum has a much greater coefficient of expansion than glass. When aluminum window frames expand and contract at a different rate then the glass pane, the seal can be compromised and with it the insulation properties.

Most all fiberglass window profiles are manufactured from the pultrusion process. The profile cross section of a window lineal is exactly the same. Most all major window companies have an in-house pultrusion operation, where they pultrude thousands of feet of window lines a day.

Hot Tubs and Spas

Hot tub and spas are another great example of fiber reinforced composites which might be used around the house. Most all above ground hot tubs today are reinforced with fiberglass. First, a sheet of acrylic plastic is vacuumed-formed to the shape of the hot tub. Then, the back side of the sheet is sprayed with chopped fiberglass known as gun roving. The ports for jets and drains are drilled out and the plumbing is installed.

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Johnson, Todd. "FRP Composites Around The House." ThoughtCo, Aug. 27, 2020, Johnson, Todd. (2020, August 27). FRP Composites Around The House. Retrieved from Johnson, Todd. "FRP Composites Around The House." ThoughtCo. (accessed March 30, 2023).