<p>In an air filter comprising a laminate of polyester or polyolefin fibres and a PTFE film, the filter is heat-treated before or after lamination. The air filter comprises a laminate of a fleece comprising fibres containing a main component from polyolefins and polyesters or a compound material of the fleece and a porous PTFE film. The total amount of gases generated by the filter is at most 20 mu g/g. Independent claims are included for the production of the above filter by heat-treating the above fleece or compound material at 80-130 deg C for 5-20 minutes and laminating the fleece or compound material to the PTFE film and alternatively by heat-treating the obtained laminate.</p>
