High efficiency particulate air filter

A filter mat effective to filter air, which comprises in the below respectively indicated proportions to one another

• (a) about 250 parts of glass micro-fibers admixed together composed of
• (i) about 50 parts of such fibers about 6,300 microns long and about 4.3 microns in diameter,
• (ii) about 50 parts of such fibers about 1,500 microns long and from about 2.17 to about 3.1 microns in diameter, and
• (iii) about 150 parts of such fibers about 1,000 microns long and from about 0.49 to about 0.58 micron in diameter;
• all intertwined with
• (b) from about 9.35 about 10 parts of a cobeat including
• (i) from about 4.68 to about 5 parts of cellulose fibers and
• (ii) from about 4.67 to about 5 parts of micro-bits of an expanded styrene-polymer, of an expanded polyolefin from the group from polyethylene through polymethylpentene or of a flexible polyurethane, the initial expanded form of each of which was non-brittle;
• and
• (c) from zero to 2 parts of an organic binding agent distributed substantially uniformly throughout the intermixture of the intertwined cobeat and intermixed glass micro-fibers without destroying the air permeability of the filter, said binding agent (i) being inert to the constituents of the filter mat and to the fluid media that is to contact the mat, (ii) having its binding effectiveness initiated by heat, and (iii) being selected from (x) such binder insoluble in cold water and soluble in hot water and (y) any of the aqueous acrylic emulsions and polyvinyl chloride emulsions used as binders, and each of which binders (x) and (y) retains its binding function on cooling.