These don't take much fabric at all; I made mine from some scraps of leftover material from a Christmas project. I used regular cotton fabric, but flannel would be dreamy, too.
Start by making your heart pattern. You can print off a heart shape from your computer, or you can go old-school and make your own; to keep the heart symmetrical, fold your paper in half, then cut out the heart. Be sure to account for seam allowances and adjust your pattern accordingly so that your finished product is the size you want. (Here's an smart tip for adding seam allowances!) I made my pattern from a Papa Murphy's Pizza flyer because it was handy. :)
You will need two hearts for each hand warmer and four hearts if you're making a set.
Place two hearts right sides together and sew, leaving a 1-inch opening for turning and stuffing. I would recommend having your opening along a straight side edge. When I made mine, I left the bottom open, which made sewing the point of the heart kind of tricky.
Trim your seams, clip your curves, and turn the heart right-side out. If you need to, use a pencil (or one of your husband's fancy chopsticks, if you're me) to help poke the fabric through. You can also use a knitting needle, but be careful not to jab it through your fabric and make a big hole.
Once your heart is turned right-side out, fill it with rice. I used the regular ol' long grain stuff. You may need to use a funnel or some rolled up paper to help you fill it. You don't want it too full, just under halfway. I used a little over 1/8 cup of rice to fill this one.
After filling, stitch your opening closed. There you have it! A lovely, Valentiney hand warmer to give away or keep for your own cold fingers. Make another one (or fifteen if you have a lot of friends) so that the recipient can have one for each hand.
To use, pop your hand warmers in the microwave for a minute and then see how they feel. If needed, nuke them a little longer. You want them warm enough to be soothing but not hot enough to inflict burns.
These are pretty quick to whip up and if you make them assembly-line style, you will have a bunch of cute hand warmers for all of your Valentines in no time!!