have other shapes for example a rectangular one and can be made from other materials the valve can also be secured to the mask by other conventional and known methods for example by polyolefins or eva based hot melt adhesives the mask is also equipped with conventional systems to enable the mask to be closely fitted to wearer 39 s face and to enable its edges to be in tight contact with the different parts of the face in particular the clip 5 improves the fit over the wearer 39 s nose whereas the bands 4 are used to position the mask snugly over the user 39 s head the bands are made from conventional materials in particular from a combination of an elastic constituent such as synthetic rubber and a thermoplastic constituent for example polypropylene chosen for its affinity with the preferred mask 39 s constituent in addition the mask is equipped on the edges with a boundary sealing layer applied all along the perimeter on panel 2 and 3 of fig2 this layer is indicated as 7 in fig2 and is drawn around the mask periphery on superior and inferior edges of the mask starting from the side joins in addition adjoining this layer a strip made from the same material 8 in fig2 and some 9 cm long is applied in the nose clip area the strip makes the mask more comfortable to wear and further on improves the seal between the mask and the face at the.