Specialists recommend a filter insert. One suggested is a washable shop cloth (blue ones) cut to fit the mask. The pocketed masks offered here will accommodate a filter. We will be offering some in the near future.
HINT: For the masks that come with elastic, there should be enough there to adjust them to the length you need. Once tied again, you can rotate the elastic so the tied end is hidden in the mask. If you have ties you can swap them for the elastic on most of these masks. Check the description carefully if this is something you might like to do.