The ornamental design for a cushion for a respiratorymask, as shown and described.
FIG. 1 is a front perspective view of a cushion for a respiratory mask according to an embodiment of our design;
FIG. 2 is a rear view thereof;
FIG. 3 is a right side view thereof
FIG. 4 is a top view thereof;
FIG. 5 is a rear perspective view thereof;
FIG. 6 is a front view of a cushion for a respiratory mask according to an embodiment of our design;
FIG. 7 is a rear view thereof; and,
FIG. 8 is a top view thereof.
The features shown in broken lines depict environmental structure only and form no part of the claimed design. Where included, dotted lines represent the border between claimed and unclaimed subject matter and form no part of the claimed design.