Medtex M5U Fabric MaskSize: M, standard size, same as surgical masks. Disposable. Tested and proven to filter 95% of 5 micron particles, even without a filter. Easy to breathe with a 3 layer muslin fabric structure, a unique feature of Medtex. Reduces the accumulation of dirt with a 3 pleat downward design. A central lock sewing technique for the strings and piping reduces the problem of the ear loops shifting. It also offers a secure fit around the cheeks by tightening