I claim the ornamental design for an attic door insulator, as shown.
FIG. 1 is a perspective view of the attic door insulator;
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; and,
FIG. 7 is a left side view thereof.
The attic door insulator is used to seal and insulate bonus room doors and any other type of door between the attic and conditioned space to save energy.