Materials that are more readily available to the public can also be effective for some folded mask designs, says Jonathan Realmuto, a postdoctoral researcher at the University of California, Irvine. For example, non-fiberglass MERV-13 filters, which are commonly used for heating, ventilation, and air conditioning systems, are particularly effective and available at most hardware stores. … A pattern developed by UC Irvine's Realmuto and his colleagues was designed to be made in emergencies using readily available items. The folds, he says, limit leakage along the mask seams. Read More