I found: "Over time, components such as the straps and nose bridge material may degrade, which can affect the quality of the fit and seal" [1] Also, some filte

I found: "Over time, components such as the straps and nose bridge material may degrade, which can affect the quality of the fit and seal" [1] Also, some filters are constructed from charged fibers and electrostatic attraction helps in the filtering [2]. I wonder if that electrostatic attraction can be lost in some way, which would help explain the expiry date. Anyway, [1] also says using expired masks may be considered in a crisis, best for training and fit testing though. [1] https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirators-strategy/crisis-alternate-strategies.html https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirators-st... [2] https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/ https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/