Winter morning dog walks. 20 degrees. My fingers went numb about three minutes in. I’d been buying those disposable hand warmer packets — the ones you shake to activate — and burning through two pairs a week at a dollar each. That’s over a hundred dollars every winter. For something I threw away after one use.

My neighbor, who walks her dog in a bathrobe at 6 AM like temperature is just a suggestion, saw me shaking a hand warmer packet. “You know those are just rice and a sock, right?”

How to make one

1. Take an old clean sock. Tube sock works best. No holes.
2. Fill it with uncooked rice. About two cups. Not instant rice — regular long-grain white rice. It holds heat longer.
3. Tie a knot in the end. Leave a little room — the rice needs space to move around.
4. Microwave for 60-90 seconds. That’s it.

The rice heats up and stays warm for 20-30 minutes. About the length of a dog walk. Or a commute to the bus stop. Or sitting in the bleachers at a cold soccer game.

Why rice works so well

Rice is dense. It absorbs microwave energy efficiently. Once heated, it releases warmth slowly — much slower than water, which cools fast. A rice sock is essentially a thermal battery. Tiny grains, massive surface area, slow release.

You can also add a few drops of essential oil to the rice before microwaving. Lavender makes it smell nice. Peppermint feels cooling and warming at the same time — weird sensation but pleasant in cold weather.

Other things you can fill it with

• Flaxseed: Holds heat even longer than rice. Slightly more expensive.
• Cherry pits: The traditional choice. You can buy bags of dried cherry pits online. They conform to your body better than rice.
• Feed corn: Larger kernels. More air between them, so the heat doesn’t last as long. But it’s dirt cheap.
• Buckwheat hulls: Lightweight. Conforms well. Doesn’t hold heat as long as rice.

The reusable difference

One rice sock replaces hundreds of disposable hand warmers. I’ve been using the same two socks for three winters. The rice gets a little dusty but still heats fine. When it stops heating well — and it will eventually, after a couple hundred cycles — you’re out a sock and two cups of rice. About fifty cents total.