there are increasing demands for higher air-to-cloth ratios at higher temperatures for dust filtration fabrics. the paper reviews the mechanisms for the initial fibrous filtration of gas stream and the effect of fiber geometry on aerosol collection efficiency prior to cake formation. the properties of conventional fibers, currently available to the trade, are reviewed and their limitations are cited for operating in a hostile flue gas environment. tensile and other properties, after cyclic acid/heat exposure, are given for other polymeric materials that are potential candidates for high temperature acid resistance filter media. properties of conventional industrial fibers are listed for: cotton; nylon; polyethylene terephthalate; orlon and dralon t(polyacrylonitriles); polypropylene; nomex (aromatic polyamide); teflon (polytetrafluoroethylene). none of these is itself suitable for bag filter application. glass fiber, coated with silicone-graphite or teflon, have been used at low air-cloth ratios as woven fabrics for bag filters. some of the new polymeric fibers considered potential candidates for filter bags are: ryton (polyphenylene sulfide); pbi (polybenzinidazole); prd-14 and 2080 (both polyimides); kermel (polyamidimide). 4 refs