Pick a durable cotton for your bean bag. The fuzzy side of sweatshirts work well. If your fabric is thin, fold it in half to double the strength.
Step 2: Measure and Cut
Your bean bag can be any size or shape. I like square ones and long skinny ones that can hang over my neck. You can measure with a ruler or eyeball it. Make the fabric twice as long as you want it to be to allow to fold it in half (just like making a pillow).
Step 3: Personalize
If you want, the bag can be personalized with an applique. For this bag, I chose an initial. make a paper stencil of your shape. Pin the stencil to a complimenting fabric and cut out the shape. Fold your fabric in half (the way it will look when it is filled) and pin on the applique. Sew on the applique. I used a whip stitch because it was easiest for me. Sew it however you like.
Step 4: Sew the Sides
Inside out the bag. Sew three of the four sides shut (assuming its a square). Turn the bag right side out.
Step 5: Fill
Fill the bag with pinto beans or rice. Don't pack the bag, let there be room for the pieces to shift around. If it is too full it won't be able to contour to your sore muscles or cold feet.
Step 6: Sew The Last Side
Fold over each piece of fabric on the fourth side (put the raw edge into the bag) Pin the pieces together and sew the last side shut.
Step 7: Microwave
Microwave the bag for about one minute (this will differ for microwaves, size of bag, and amount of filling). Enjoy the warmth.