玻璃本身是不燃材料，但当它作为围护材料时由于火灾发生时的环境温度高于玻璃的软化点，玻璃围护坍塌，已不能阻挡火势，准确地说防火性能是取决于耐火极限。防火玻璃国家新标准《建筑用安全玻璃》（GB15763.1－2008）将防火玻璃的性能分为A类和C类。其中A类为隔热型防火玻璃，其耐火极限分0.5h，1.0h，1.5h，2.0h，2.5h，3.0h六个等级。C类为非隔热型防火玻璃，其防火时间设置了4个等级：0.5h，1.0h，2.0h，3.0h。所谓隔热性防火玻璃是指其耐火性能同时满足耐火完整性和耐火隔热性的玻璃。如果只能满足耐火隔热性的就称非隔热性玻璃。
    U型玻璃的耐火极限为0.75h，当不能满足设计时可加贴防火膜或与平板铯钾防火玻璃配合使用。

Glass itself is non-flammable material, but when it is used as enclosure material, because the ambient temperature is higher than the softening point of glass when the fire occurs, the glass enclosure collapses, which can not stop the fire. Precisely speaking, the fire resistance depends on the fire resistance limit. The new national standard of fire-proof glass, Safety Glass for Buildings (GB15763.1-2008), classifies the performance of fire-proof glass into A and C categories. Among them, Class A is heat-insulating fire-proof glass. Its fire resistance limit is divided into six grades: 0.5h, 1.0h, 1.5h, 2.0h, 2.5h and 3.0h. Class C is non-insulating fire-proof glass. Its fire-proof time is set up in four grades: 0.5h, 1.0h, 2.0h and 3.0h. The so-called insulating fireproof glass refers to the glass whose fireproof performance satisfies both fireproof integrity and fireproof insulation. If it can only meet the requirements of fire resistance and heat insulation, it is called non-insulating glass.

The fire resistance limit of U-shaped glass is 0.75h. When it can not meet the design requirements, it can be used with fire-proof film or with flat Cesium-Potassium fire-proof glass.