Cushion for respiratory mask

FIG. 1 is a front perspective view of a cushion for a respiratory mask according to our new ornamental design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side view thereof, with the left side view thereof being a mirror image thereof; and,

FIG. 7 is a rear perspective view thereof.

The broken lines represent environmental structure and do not form a part of the claimed design.