Abstract: Provided is a filter favorably used in high-temperature long-term exposure conditions, for example, in coal boilers, cupola furnaces for steel and cast iron production, cement kilns, aggregate drying furnaces, furnaces for non-iron metals, etc. For the filter, provided are a filter material comprising a web or a web and its support, which contains a polycyanoaryl ether in an amount of not smaller than 5% by weight relative to the weight of the filter material; and a filter material comprising a substrate of polycyanoaryl ether fibers or of polycyanoaryl ether fibers and other organic fibers, and a web of at least one type of fibers selected from polycyanoaryl ether fibers and other organic fibers, wherein the amount of the polycyanoaryl ether fibers is not smaller than 5% by weight relative to the total weight of the substrate and the web.