F-Series · Fiberglass
Glass that behaves like a wall.
Pultruded fiberglass expands and contracts almost exactly like the glass it holds, so seals last and frames stay slim. Fifteen systems from the GR65 minimal-frame window to the GR145 sliding wall.
A window has always been the weak point in the wall — the thermal hole every heating and cooling dollar leaks through. Paired with ZERO 04 vacuum glazing, the glass itself reaches R-23 at the center, and a complete GR85 fixed window reaches R-11.8 (U 0.085). At that point the opening stops behaving like a gap you glazed over and starts behaving like the wall itself: no cold edge, no condensation line, no penalty for going bigger. You get the daylight and the view without giving back the envelope.
The lowest U-factor in our range
ZERO 04 hybrid vacuum glass reaches U 0.044 at the center of the glass, and complete windows reach R-12.
Glass packages › The warrantyOn the vacuum glass
A 25-year limited warranty on the vacuum insulating unit, covering loss of vacuum and seal failure.
Warranty terms › The frame- Four times stronger than aluminum
- Expands with the glass, so seals stay tight
- Will never rot, rust or warp
- Insulates without a thermal break
- Built for salt air and the coast
- Fire-resistant and recyclable
Pultruded fiberglass, tested to CW-PG45 for air, water and structural load.
Why fiberglass ›Why fiberglass
Pultruded fiberglass is the reason the F-Series behaves the way it does.
Fiberglass is inherently strong, dimensionally stable, and built to perform in all climates. It expands and contracts at nearly the same rate as the glass it holds, so seals stay tight through decades of seasonal swings.
Certified Passive House Component: the GR85 dual-action window earns the Passive House Institute’s highest efficiency class, phA, for cold and cool, temperate climates. See the certified values ›
All F-Series systems
Windows, doors, and sliding and lift-slide systems. Every fiberglass frame suits Passive House work.
GR60 & GR65
60–65 mmSlim frames for the most glass and daylight
GR65 Fixed Window
GR65 Dual Action Window
The GR60 and GR65 are the narrowest fiberglass frames we make, drawn for the most glass in a tight elevation.
Frame width comparisons ›
GR60 Swing Door
GR70
70 mmA deeper frame for hybrid vacuum glass
GR85
85 mmThe lowest U-values in the range
GR90 – GR145
90–145 mmSliding windows, sliding doors and lift-slide glass walls
Sustainable by material
Fiberglass takes less energy to produce than aluminum, gives off zero VOCs in service, and is recyclable at the end of its life. A durable envelope with a lighter footprint, built to outlast the building's first renovation cycle.