Winter Camping

The Humble Hot Water Bottle is the Ultimate Cold-Weather Sleeping Trick

Too cold to catch some rest? This simple hack provides a long-lasting boost of warmth—and works as well at home as it does on the trail.

You’re in a pickle: You’re nestled in your sleeping bag, you’re wearing all of your layers, and you’re still too cold to sleep.

No matter how well you’ve planned, occasionally you’ll find yourself sleeping out in temperatures lower than what you packed for. While most cases of underpacking aren’t dangerous—your sleeping bag will stop being comfortable well before you risk hypothermia—it can spell frigid feet, cold fingers, and sleepless nights.

In situations like this, we turn to a decidedly old-school solution: the humble hot water bottle. Used to warm beds across the world for hundreds of years, slipping a container of hot water under your covers is still one of the most effective ways to cozy up your sleeping space. It’s also easy to do on the trail. Just follow these steps for a nicer night out.

  1. Grab a suitable bottle. You’ll want something uninsulated (lets the heat out) with a secure, screw-on cap (keeps the water in.) It should also be on the bigger side (more water means longer-lasting heat.) Nalgenes and other screw-top, hard plastic bottles are ideal; metal bottles will work in a pinch, just be careful not to burn yourself on them. (Avoid disposable plastic bottles, which can warp or melt and spring a leak when exposed to extreme heat.)
  2. Just before heading to bed, heat up your water to a rolling boil using your stove. Carefully pour it into the bottle and secure the cap. Test the bottle’s temperature with the back of your hand. If it’s uncomfortable to touch, wrap it in a t-shirt or whatever spare layer you have on hand.
  3. Slip the bottle into your bag by your core or inner thigh and settle in for a toasty night’s sleep. (Depending on the temperature, you may need to get up midway through the night to refresh your bottle’s hot water.)

To Drink or Not to Drink?

No one likes to waste water. But those of us who remember the panic around bisphenol-A (BPA), a chemical used in some food containers that some studies have linked to cancer, heart disease, and reproductive abnormalities, may be hesitant to drink hot water from a plastic bottle. The good news: In a study published in 2011, a team from the University of Cincinnati College of Medicine found that Tritan plastic (the stuff hard Nalgenes are made of) and stainless steel water bottles didn’t leach BPA even when filled with boiling water. If your bottle is marked BPA-free, you probably don’t have anything to worry about.