The recommendation for the general public to wear face coverings is intended to reduce the transmission rate of individuals carrying the disease unknowingly. It's meant to serve as a reminder to maintain social distancing protocol. Materials with a tighter weave or that are less porous have been shown to be more effective in actually stopping particles from traveling through the material. I've read studies that suggest t-shirt masks are a good material choice because they are comfortable and easy to breathe through. I've read other studies suggesting that knit fabrics are useless. I am operating under the belief that something is better than nothing. I would suggest using a knit face mask only when you are able to add a tightly woven (quilting cotton, flannel) or non-woven (carbon filter, HEPA filter) material inside the mask. This no sew t-shirt mask has a pocket where a filter can be used.