We’ve all been there: shivering in our sleeping bags for what seems like hours before we finally drift off to sleep. I’d put up with it for a long time, as I’m always trying to find a balance between weight, packability, and warmth in a sleeping bag. Even with a well insulated bag, it’s difficult to warm up and stay warm after being battered to near hypothermia by the elements.

My biggest problem in that respect is my feet, which are usually freezing when I crawl into the bag. It wasn’t uncommon for me to wake up several times during the night with numb toes. I have to credit my hunting partner Steve for the solution to my problem; a while back he told me this extremely simple but effective tip.

On most of the hunts I go on, especially backpack hunts, I carry a couple of Nalgene bottles. Not only are they tough, but they can serve as a sleeping bag heating catalyst. It’s about as simple as it gets, but makes all the difference in the world. When the mercury is dropping hard at night, just boil a pot of water right before you go to bed. As soon as the water is boiling, dump it in an empty nalgene bottle, tighten it up, and throw it in the bottom of your sleeping bag. When you crawl in, your feet will be toasty, and will continue to stay warm throughout the night. Plus, the bottle acts as a fairly long-term warmer. The plastic provides enough insulation to keep the hot water from burning your feet, and also produces a slower, steady release of that heat. The area around your feet quickly heats up to the same temperature as the bottle, and once that thermal equilibrium is reached, the only heat lost from the water is the little bit that is lost through the insulation of the sleeping bag. I know we can all do without a lecture, but I have to use my engineering degree for something, right?

All in all, this is a great little trick that works like a charm, and quickly brought an end to my wimpy complaining!