Fibrous filtration face mask having a new unidirectional fluid valve

A filtering face mask that has a mask body and an exhalation valve. The mask body is adapted to fit over the nose and mouth of a wearer. The exhalation valve is attached to the mask body and has a valve seat that includes a seal surface and an orifice that is circumscribed by the seal surface. The valve also has a single flexible flap that has a fixed portion and a free portion and first and second opposing ends. The first end of the single flexible flap is associated with the fixed portion of the flap so as to remain at rest during an exhalation, and the second end is associated with the free portion of the flexible flap so as to be lifted away from the seal surface during an exhalation. The second end also is located below the first end when the filtering face mask is worn on a person. The flexible flap is positioned on the valve seat such that the flap is pressed towards the seal surface in an abutting relationship therewith when a fluid is not passing through the orifice. A valve cover is disposed over the valve seat and comprises: an opening that is disposed directly in the path of fluid flow when the free portion of the flexible flap is lifted from the seal surface during an exhalation; a fluid impermeable ceiling that increases in height in the direction of the flexible flap from the first end to the second end; and cross members that are disposed within the opening of the valve cover.