The ornamental design for a cushion for a respiratorymask, as shown and described.
FIG. 1 is a rear 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 front view thereof
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a front perspective 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.