Polyurethane pultrusion windows (GFRP-PU)

Polyurethane pultrusion windows are windows whose frame and sash profiles are pultruded from continuous glass fiber and a polyurethane (PU) resin matrix instead of the conventional polyester or vinyl ester resin. The material is abbreviated GFRP-PU (glass-fiber-reinforced polyurethane), sometimes written GFRPU or PU fiberglass. The pultrusion process is the same continuous pull-through-a-heated-die method used for all FRP profiles; the difference is the resin chemistry, which is injected into a closed box rather than picked up in an open bath. The result is a window profile with higher cross-fiber strength, higher achievable glass content, and thinner walls than a standard polyester pultrusion, while keeping the ~0.3 W/m·K thermal conductivity that makes fiberglass frames insulate roughly 500× better than aluminum.

GFRP-PU stands for glass-fiber-reinforced polymer with a polyurethane matrix. You will see the same material written GFRPU, PU-FRP, or PU fiberglass in specifications. They all refer to pultruded profiles where continuous E-glass reinforcement is bonded by polyurethane resin. In fenestration, a 'GFRPU fixed window system' or 'GFRP-PU tilt-and-turn window' simply means the frame, sash, mullion, and transom profiles are polyurethane pultrusions. F1 Composite's severe-cold window references (including the Qinling Station Antarctic installation and the Wanhua Yantai zero-carbon community) are GFRP-PU systems.

Three practical differences drive window design. First, strength across the fiber direction: PU's tougher matrix gives the profile markedly higher transverse and interlaminar strength, which is what resists screw pull-out at hinges and multi-point locks, and corner-joint stress in an assembled sash. Second, wall thickness: because the matrix is tougher, PU profiles can be pultruded with walls down to roughly 2 mm and glass content up to about 80% by weight, giving slimmer sightlines and a lighter sash for the same stiffness. Third, processing: PU is injected in a closed die box with styrene-free chemistry. The trade-off is cost: PU resin systems price above polyester and vinyl ester, which is why F1 reserves them for performance-critical fenestration rather than commodity structural profiles.

A small group of pultruders worldwide run polyurethane window lines, because PU requires dedicated closed-injection equipment and tighter process control than open-bath polyester. FengDu produces the GFRP-PU profiles; F1 Composite supplies them internationally as profile sets for local fabricators or as factory-assembled, glazed, and leak-tested window and door units delivered DDP. The same profile set sits behind PHI Component Certificate 2491wi03 (U_w 0.78 W/m²·K, phB efficiency class for the cool-temperate climate zone).

Cold-climate projects require a complete window and installation review. F1's 90-series GFRP-PU frame holds PHI Component Certificate 2491wi03 at U_w 0.78 W/m²·K in the phB efficiency class for the cool-temperate climate zone, and the same system is installed at Qinling Station in Antarctica against a −60°C design low. Because the polyurethane matrix keeps its impact strength in deep cold and the profile needs no steel reinforcement, the frame carries no metallic thermal bridge: the failure point that limits aluminum and steel-reinforced PVC frames in passive house detailing.

At the profile level, yes: polyurethane resin systems are the most expensive of the three common pultrusion matrices, above vinyl ester and polyester. At the installed-window level the gap narrows, because PU's thinner walls use less material per meter, the sash needs no steel reinforcement, and the higher hardware pull-out strength simplifies corner and lock detailing. For projects where the driver is certified passive-house performance, deep-cold durability, or slim sightlines, the PU premium is typically small against the whole-window cost, which is dominated by glazing and hardware. For budget-driven projects in mild climates, a polyester or vinyl ester FRP frame, or PVC, remains the economical choice.