For my own masks I use a 100% Cotton Batting (from Joanns) cut them into about a 6X6 square or 5X5 pieces and insert them in my mask. (I inserted one batting into one of the masks for sample) You can also buy the inserts for these if you can find them. I've seen people use several layers of paper towels or even coffee filters to insert and you just throw them out. See last photo, it has a cotton batting insert in it. I do not make the inserts, each person can add any type of insert to these masks.
If you have any questions please ask before bidding. Thanks for looking at my item.