Chongqing Mexin Best Doors and Windows is the fire-door arm of the Mexin group (重庆美心), among the largest domestic door manufacturers in China. Its foam- and honeycomb-core steel fire doors are listed in the Intertek Directory of Building Products under SpecID 22241 and carry the Warnock Hersey certification mark for single and paired three-hour positive-pressure assemblies, with temperature rise above 650°F at thirty minutes. The listing states vision panel limits of 1296 square inches for twenty and forty-five minute openings and 100 square inches for sixty and ninety minute openings.