Who here knows how long the NATO filters on the Israeli gas masks last?  They use the screw on can type.  I also have one with cheek filters coming.  Haven't found any info on this yet.  As a side note I was at a gunshow this weekend and a milsurp seller had taken the filter cans out of the wrap and some had their seals removed.  I know that exposure to even clean air will make them ineffective after a period of hours due to the moisture.  I think some people may have bought some dud filters from that guy today.