Glazing is an integral part of modern design. From a thermal standpoint, glazing and its structure or frame is the weakest point of a wall assembly.¹ A double-glazed vinyl window with argon’s U-factor (i.e. thermal transmittance) is typically around 3 W/(m² K). This means the window will gain or lose around 3 W per m² per degree Celsius. An efficient fibreglass window system’s U-factor can be as low as 1 W/(m² K). An aluminum curtain wall system can range as high as 4 W/(m² K). On the other hand, the U-factor of a 152-mm (6-in.) steel stud, with batt and exterior continuous insulation, can be around 0.4 W/(m² K).