Nasal masks and associated filters and structures are disclosed. One disclosed nasal mask includes a filter sheet comprising an inner side and an outer side, a pair of slits on the filter sheet, a first set of attachment means distributed on the inner side of the filter sheet, and a second set of attachment means distributed on the outer side of the filter sheet. The filter sheet is adapted to be bent along the pair of slits so that at least one attachment mean in the first set of attachment means is attached to at least one attachment means in the second set of attachment means.