These are simple 3 layer masks made using CDC and Health Canada guidelines and are intended for short outings, when it is absolutely necessary to do so. They are not designed to replace a medical grade face mask. They are not intended to encourage anyone to reduce any requirements for social distancing and they must be washed after each use.
Recent studies seem to be indicating that a combination of fabrics result in the best non-medical masks. Researchers point out that tightly woven fabrics, such as cotton, can act as a mechanical barrier to particles, whereas fabrics that hold a static charge (like polyester) serve as an electrostatic barrier. A third layer of non-woven material adds extra protection while maintaining breathability.
We use of these fabrics in various combinations for all of our masks, including a permanent non-woven filter material layer. We have opted to not use removable filter as it may lead to users simply changing the filter and not properly washing the mask between uses, or wearing a mask without filter material should they run out of disposable filters.
More importantly you mask must fit snugly around your face. Any gaps that allow the wearer to breath around, rather than through, the mask can make them up to 90% ineffective.