Our masks do not have a pocket for filters but do have an area where a filter can be tucked in to the interior of the mask. According to the NY Times' article, A User's Guide to Face Masks it states the below.
"Coffee filters and paper towels: The C.D.C. suggests inserting a coffee filter into your mask for extra protection. Missouri University of Science & Technology scientists found that using three coffee filters made it difficult to breathe. Adding a layer of paper towel in between two layers of fabric could make your homemade mask more efficient. An engineer at an air purifier firm ran his own test and found a single paper towel filters 23 percent of 0.3 microns and two paper towels filtered 33 percent."