The mask already comes with 4 layers of filtration but you also have the option to add another filter to the mask through an opening it has on the bottom. This is also meant for when the polypropylene filters inside the mask begin to wear and tear, you can still use this mask by simply adding any filter or single use masks The mask is made up of 2 layers of polypropylene, and 2 layers of high count cotton. Our cotton fabrics range from 85-100% cotton/poly-cotton.