Do you wish to be exterior all winter? Carry your thermos.

Sure, long underwear is nice, but have you ever warmed up with miso soup in the middle of your snowshoe tour? On bitterly cold days, it is much easier to heed the call of the wild over the call of the couch knowing you are always within easy reach of a hot drink. So get your thermal game.

While warm drinks alone won’t protect you from hypothermia, they are part of a multi-tiered approach to treating backcountry hypothermic sufferers, says Zack Fuecker, a Minnesota wilderness first responder. Just know that shaking, which is your body’s primary method of keeping you warm when not properly dressed, is a real drain of energy. So it is more the carbohydrates in the thermos that help in such situations than the liquid that actually warms you from the inside out. And, according to Patrick Wilson, professor of exercise science at Old Dominion University and author of The Athlete’s Gut, while there isn’t a lot of research showing that warm fluids improve athletic performance, they may keep you hydrated – but not for the reasons who have favourited You have to consider. “Any of the benefits would likely be more perceptual, such as increasing your urge to drink,” he says. When returning from winter adventures that barely touched your hydration, bring a warm drink to make drinking more attractive.

To get the most out of your thermos (and what’s in it), you need to understand thermodynamics. Heat is essentially energy. When a liquid is hot, the molecules that make up that liquid vibrate at a higher frequency than when that liquid is cold, says Kyle Overdeep, a scientist who specializes in this branch of physics. When a hot drink comes in contact with a cold surface – the wall of your drinking cup, for example – these fast-vibrating molecules collide with the slow-moving ones, heating the surface. How quickly a surface transfers heat depends on the density of that surface, explains Overdeep. Air, with its low density, is an ideal insulator, which is why puff coats work so well. What is even less dense than air? A vacuum.

Between the inner and outer walls of a vacuum-sealed thermos is a tiny cross-section from which all of the air was sucked out directly. In a vacuum, these energetic molecules in your drink have even fewer atoms to bump into. Voilà! Your drink will stay hot longer.

Now that you understand how your thermos works, here’s how you can tweak it.


Your coffee will drain valuable energy and heat the side wall of your thermos. When you have ten minutes, fill your thermos with hot water and let the inner wall warm up. Then empty it and refill it with the liquid of your choice.

Fill up

According to David Cipoletti, associate director of advanced development at Hydro Flask, volume is important when it comes to keeping something hot. Because heat transfer takes place at the surface of liquids, three ounces of liquid swirling around and in contact with the walls of your thermos will lose heat much faster than a filled 48-ounce container that only holds a significant portion of the liquid in Contact with other liquids.

Pack Smart

Water stores energy well, says Cipoletti, so tea and coffee generally stay hot for a long time. Packing food in a thermos becomes more complicated. For example, scrambled eggs have a lot of air pockets and can lose heat more quickly than something denser like soup.

Think about food safety (even in winter)

The food hazard zone – where bacteria thrive – is between 40 and 140 degrees Fahrenheit, says Sean O’Keefe, who works in the Department of Food Science and Technology at Virginia Tech University. If you want to eat hot food in the backcountry, you have to keep it really hot. “Soup or stew are fantastic media for growing bacteria. They have nutrients, their pH is near neutral, and they’re usually consumed warm, ”he warns. If you’re unsure of how well your thermos is working, it’s better to pack hot water and mix it with dehydrated soup packages on the way than to wrap beef stew on the way.

Be gentle

After companies create a vacuum between the two layers of a thermos, they need to seal the whole thing with super-tight welds. But the air is sneaky. Over time, molecules can slip through tiny cracks in the weld seams and destroy this vacuum. This is especially likely if you are like me and have a tendency to drop things. The less you mess around with your thermos, the longer the welds will last. For your information: The dishwasher is fine. It won’t break the seal.

Tighten the cap

There’s no vacuum at the top of a thermos, so this is a major leak point for heat, says Cipoletti. Unfortunately, the heat rises, which makes the problem worse. The quality of your lid is less important when it comes to cold storage. If you want to keep things hot, look for a lid that has some extra insulation in it. Hydro Flask, for example, offers lids with “honeycomb” insulation, which essentially introduce a layer of air into the lid. Pour your liquid into your thermos, screw the lid on as tightly as you can, and don’t open it until you’re ready to pour yourself a mug.

Make something tasty

This will help you get your butt out the door even on the coldest days and it will encourage you to consume what you have and keep your energy levels up to date. At the Retreat, Links and Spa at Silvies Valley Ranch in Seneca, Oregon, guests are sent on sleigh rides with thermoses of this homemade hot chocolate.

Oz the favorite chocolate from Clydesdale

Heat one for one serving Cup of whole milk in a small saucepan over medium heat until it begins to steam. Stir in a quarter of a tablet of Mexican Ibarra chocolate and a pinch of kosher salt. (At the ranch, they grind the chocolate in a food processor to make it dissolve faster.) Pour an ounce of Ancho Reyes chile liqueur into mugs. For the full tailgate version of this drink, add whipped cream and roasted marshmallow.

Three thermoses that we recommend

(Photo: Courtesy GSI Outdoors)

GSI Outdoors Microlite 1000 Twist ($ 35)

GSI Outdoors claims the Microlite will keep drinks hot for up to 18 hours and cold for up to 32 hours, and our tests (OK, we forgot we left this thermos in a pack overnight) showed that drinks were incredibly hot stay a long time. A reliable screw cap and super light stainless steel construction make it ideal for being pushed around in a pack.

stanley-unbreakable-jar_h.jpg(Photo: Courtesy Stanley)

Stanley 17-Ounce Master Unbreakable Food Jar ($ 60)

This Stanley vacuum insulated food jar is one of our Gear Guy’s favorites. It “knocked out the competition in the thermoregulation test,” he wrote. He also appreciated its weight and visual appeal. It’s a great option for carrying soups and hot items, but we found it a little difficult to clean and eat due to the small diameter of the mouth.

ecovessel-trimax-growler_h.jpg(Photo: Courtesy of EcoVessel)

EcoVessel 64-ounce Boss Insulated Growler ($ 60)

According to EcoVessel, the Boss keeps drinks cold for up to 150 hours and hot for up to 24 hours, although we haven’t tested them up to these limits. It kept our beer cold on the rock on long summer days and our cider very hot during the parking lot in the ski area. There are two rotating lids: one with a silicone drinking lip that we like to pour and a wider one that comes in handy when it’s time to fill it up.

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Main photo: Ben Girardi / Cavan

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