Frame materials compared

Fiberglass, thermally broken aluminum, wood, aluminum-clad wood and uPVC, honestly compared.

Pultruded fiberglass

Fiberglass profiles are pulled continuously through a resin bath and heated die, producing a stiff, hollow section with glass fibers running its full length. The material's coefficient of thermal expansion is nearly identical to glass, so the frame and the glazing move together through the seasons and seals last. Conductivity is low enough that no thermal break is needed. It does not rot, corrode or creep, takes any paint or powder coat, and is fully recyclable as filler. Its limits: profile geometry is constrained by the pultrusion process, and joinery requires mechanical corners rather than welds. GlasFëns F-Series frames are fiberglass-reinforced polyurethane pultrusions by G-Ren with an ASTM C518 conductivity report on file.

Thermally broken aluminum

Extruded aluminum with a polyamide or polyurethane strut separating the interior and exterior halves of the profile. Strong, slim, dimensionally precise and available in any color; the right choice where impact ratings, large spans or hurricane wind loads govern. Thermal performance depends entirely on the break and the glazing, and the interior surface is the coldest of any frame material. Our A-Series uses thermally broken aluminum for hurricane and coastal projects.

Wood

Beautiful, warm to the touch and a good insulator, but exposed exterior wood needs finishing every few years, and species, finish and detailing decide its life. Best for historic replication where the appearance is the point.

Aluminum-clad wood

Wood inside, an aluminum skin outside. Extruded cladding is far more robust than roll-formed sheet. Maintenance is low, but the cladding adds cost and a conductive path at the perimeter.

uPVC (vinyl)

Inexpensive, low-conductivity and low-maintenance, and the most common frame in North American housing. Limits: large thermal expansion (three to seven times that of glass), which stresses seals; sagging and creep in large or dark-colored units; limited colors; and embrittlement with UV over time.

Summary

• Lowest conductivity and best dimensional stability: fiberglass.
• Highest strength and impact capacity: thermally broken aluminum.
• Lowest cost: uPVC.
• Best for historic appearance: wood or aluminum-clad wood.

← Air infiltration and the air-barrier interfaceInstallation →