Filtering face mask that has a new exhalation valve

A filtering face mask that comprises:

• (a) a mask body that is adapted to fit over the nose and mouth of a person and that has a filtering layer for filtering air that passes through the mask body;
• and
• (b) an exhalation valve that is attached to the mask body, which exhalation valve comprises:
• (i) a valve seat that comprises an orifice, a seal surface surrounding the orifice, and a flap retaining surface;
• and
• (ii) a single flexible flap that has a stationary portion and one free portion and a circumferential edge that includes stationary and free segments, the stationary segment of the circumferential edge being associated with the stationary portion of the flexible flap so as to remain in substantially the same position during an exhalation, and the free segment of the circumferential edge being associated with the one free portion of the flexible flap so as to be movable during an exhalation, the free segment of the circumferential edge being disposed beneath the stationary segment when the valve is viewed from the front in an upright position;
• the flexible flap being secured to the valve seat non-centrally relative to the orifice at the flap retaining surface, which flap retaining surface and seal surface are nonaligned and positioned relative to each other to allow for a cross sectional curvature of at least the one free portion of the flexible flap when viewed from the side in a closed position, the nonalignment and relative positioning of the flap-retaining surface and the seal surface also allowing for the one free portion of the flexible flap to be pressed against the seal surface when a wearer of the mask is neither inhaling or exhaling and to allow for the one free portion of the flexible flap to be lifted from the seal surface during an exhalation.