This is an inline filter commonly used for a CPAP machine or ventilator as a bacterial/viral filter. There are also some 3D printed designs to use these as the filter for a snorkel mask.
If you have a CPAP machine this will provide filtered air to the mask. These come in individually factory sealed and EO sterilized packs.
There are also some groups looking at using these for a mask filter alternative. One side is 22 mm inner diameter and the other side is 22mm outer diameter.
Two for $2.