Read a few articles recently that have highlighted the number of poorly made, or counterfeit, masks on the market. It seems that many of them simply don’t provide the filtration to keep you safe.
Here’s an article that may help when purchasing masks:
Another with specifics to look for.
This one is produced by the Dept of health in Valencia and is far more detailed, showing the packaging of crap or fake masks, as reported by various health organisations across Europe. It’s in Spanish, but basically if your box of masks is in here, you been sold a pup.