The ornamental design for an insulated flask, as shown and described.
FIG. 1 is a front elevational view of an insulated flask showing my new design;
FIG. 2 is a right side elevational view thereof, the left side elevational view is a mirror image;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a partial cross-sectional view thereof taken on line 6--6 of FIG. 4 with the stopper or plug shown in full side elevation and the insulating glass liner and associated seals removed for clarity of illustration;
FIG. 7 is a rear elevational view of a modification of my new design showing the stopper or plug with two handles instead of one; and
FIG. 8 is a top plan view of FIG. 7, it being understood that the remaining views of the modified design not shown are similar to those in FIGS. 1-6.