The ornamental design for a boot warmer, as shown and described.
FIG. 1 shows a right side of a boot warmer, embodying my new design, the view from the left side being a mirror image thereto;
FIG. 2 shows a top plan view thereof;
FIG. 3 shows a bottom view thereof;
FIG. 4 shows an end view thereof, taken from the left side as depicted in FIGS. 1-3; and,
FIG. 5 shows an end view thereof, taken from the right side as depicted in FIGS. 1-3.
The invention is of an ornamental design for a boot warmer, comprising a quantity of clay, sand, or similar substance(s) encased in one or more bags sewn of fabric or like material. The boot warmer of the invention is used by heating it in a microwave oven or otherwise and placing it in a ski boot or the like to warm it prior to being worn.