A few years ago I made myself a small microwavable rice filled pad to heat up for my feet, back, etc. The design was very simple, just a rectangle made from a queen size pillow case folded up a few times, filled up halfway with uncooked rice and sewn shut. The rice could flow freely within the pillow so if I wanted it flat, I had to put it down and smooth it out with my hands. Since at that time I wanted it to be versatile, this was fine. Now I have decided I need a different design more suited to keeping both the top and bottom of my feet warm in the winter while I'm at my computer desk.
I'm not very good at explaining my design so go grab a hand towel, lay it on the floor, put your feet on it about an inch from one of the short ends, and then fold up the end farthest away from you so it covers up the top of your feet. Got that? Now imagine that the towel is sectioned off into several sections and has rice inside with more rice on the part that is underneath your feet. The width is such that the sides will overlap when the pad is folded over the top of your feet but the sides will not be sewn together to create a pocket.
Be sure to insert your pad into a clean pillowcase to keep it clean as you would need to remove all the rice before you could wash it if something got on the rice pad. Anyway, just thought I'd share if anybody is trying to save on their heating bills and still keep their feet warm this winter.