| abstract |
A mask for being worn over the nose and mouth of a wearer, and a panel having sufficient transparency to permit visual observation of the mouth of the wearer. The panel is formed from first and second overlying transparent, pleated films perforated with elongate slits sized to permit two-way transit of gases, but not liquids, under atmospheric pressure. The first and second films each include a multitude of projections for maintaining between the first and second films a multitude of tortuous flow paths for permitting respiratory gas flow through the panel. |