Window and door openings are the biggest thermal bridges in building envelopes. Ordinary steel and wood-plastic composite subframes have high thermal conductivity, allowing hot and cold air to continuously penetrate, causing condensation and soaring energy consumption. Graphite polystyrene subframes, using high-density graphite polystyrene as the base material, are specifically developed for passive houses and ultra-low energy buildings, cutting off thermal bridges at the source. They are now included in the recommended products for building energy efficiency standards in severely cold regions.

According to GB/T 39866 "Technical Requirements for Subframes of Building Doors and Windows", energy-saving graphite polystyrene subframes have strict mandatory indicators: apparent density ≥150kg/m³, thermal conductivity ≤0.06W/(m・K), 24h water absorption rate ≤1.5%, screw holding force ≥1400N, and compressive strength up to 2000kPa, balancing the two core requirements of high load-bearing capacity and ultra-low thermal conductivity. Unlike ordinary thermal insulation foam, graphite polystyrene subframes are high-density modified profiles that can stably support triple-glazed heavy-duty energy-saving doors and windows, and do not deform or loosen under long-term high and low temperature cycles, solving the industry problem that lightweight thermal insulation materials cannot fix the window frame.

The core advantages lie in thermal performance: the thermal conductivity of the steel subframe exceeds 40W/(m・K), making it extremely easy to form through thermal bridges; the wood-plastic subframe has limited thermal insulation performance and is prone to mold and expansion in long-term damp conditions; the graphite polystyrene subframe, relying on the graphite infrared reflection structure, significantly reduces the linear heat transfer coefficient Ψ at the opening. According to thermal simulation calculations, when combined with high-performance thermally broken aluminum windows and doors, the overall heat transfer coefficient of the entire window can be reduced by 0.2–0.4W/(㎡・K), reducing indoor heat loss in winter and blocking the infiltration of high outdoor temperatures in summer, thereby reducing the overall building heating and cooling energy consumption by more than 20% from the window and door components.

With a comprehensive upgrade in environmental adaptability, it boasts B2-level flame retardant performance, producing no smoke and low toxicity upon contact with fire. Its closed-cell, dense structure provides waterproofing and moisture resistance, ensuring stable use in both rainy southern regions and frigid northern environments. The dimensional change rate under repeated high and low temperatures is ≤0.2%, preventing gaps and warping even after years of exposure to varying temperatures. The accompanying installation process is mature, with the subframe pre-embedded within the wall insulation layer during construction. Combined with a waterproof vapor barrier and sealant, it forms a complete airtight structure, eliminating water seepage and air leakage from openings and preventing the potential for mold growth inside the wall.

Currently, graphite polystyrene (PPS) subframes are widely used in passive house demonstration projects in Tianjin Eco-City, Xiong'an New Area, and the frigid Northeast region, and are suitable for various ultra-low energy consumption projects such as residential buildings, office buildings, schools, and healthcare facilities. Driven by dual-carbon energy-saving policies, traditional metal subframes are gradually being phased out, and graphite PPS subframes, with their integrated performance of heat insulation, load-bearing capacity, and durability, have become an essential component for high-end energy-saving doors and windows.