Ceramic membranes are effective to reduce PM2.5 emission when used for hot flue gas filtration. The properties of the sealing material play a decisive role in filtration efficiency. However, there are few studies on sealing materials for hot flue gas filtration above 700 ℃. This investigation was performed to develop flexible sealing materials which can be used for a long time at high temperatures. In order to obtain sufficient mechanical strength and continuous flexibility, three kinds of binders were selected as coating binders. The sealing materials based on high silica fiber fabric and aluminum silicate fiber fabric were successfully prepared. The effect of aging on mechanical properties and microstructural characteristics of the composites subjected to coating had been investigated by XRD, SEM and EDS. The results show that waterborne polyurethane (WPU) is a suitable coating binder for the sealing materials, which can be used for a long time at 1 000 ℃ and 700 ℃, respectively, without significant decrease in strength. However, the other two binders, aluminum dihydrogen phosphate and aluminum chromium phosphate will weaken the flexibility, resulting in frangibility and reducing sealing performance. The developed composites possess required thermo-stability and desired mechanical strength as flexible sealing materials, indicating their strong application possibility in hot flue gas filtration.