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Forty Below’s Winter Water Bottle Insulation System

Forty Below Winter Water Insulators

You need to insulate your water bottles in winter or your drinking water will freeze. The best way to do this is with a neoprene overcover that you can open without taking off your gloves. The overcover and bottle can be attached to the outside of your backpack for easy access or stored inside, where it will stay warmer for far longer.

There are 3 things wrong with most winter water bottle insulation systems today.

  1. You need to take off your mittens or gloves to unzip the water bottle insulation sleeve.
  2. You need to stop and take your insulated water bottle out of your pack because you can’t reach it while you’re moving.
  3. You need to take off your mittens or gloves to unscrew the Nalgene bottles that most people use in winter.

If you are mountaineering or winter hiking there are a lot of times when you don’t want to take off your mittens or gloves due to extreme cold or wind chill. Stopping to get a water bottle out of your pack is also inconvenient because you get cold when you stop moving. But, If you have to stop to get your water bottle out of your pack every time you need a drink, you probably won’t drink often enough and you can become rapidly dehydrated. The fact is, that continuous hydration, at a rate of 1 liter (quart) every two hours or 4 oz every 15 minutes, is required during winter sports such as mountaineering, snowshoeing, or winter hiking since your body loses moisture much faster in cold weather.

But don’t despair. Joel Attaway, at Forty Below has designed a water bottle parka system that overcomes all of these design issues. Forty Below is a small cottage industry manufacturer, well known within the mountaineering community for ultralight climbing equipment that is designed to protect you in extremely cold weather conditions.

Forty Below sells a closed cell foam water bottle parka called a Bottle Boot that uses a velcro closure system instead of zippers and can be hung from your backpack hip belt for easy access. I’ve used them for several years on winter hiking and mountaineering trips and never had to stop moving or take off my gloves when I needed a drink. At $19.95 each (1 L size), they can accommodate Nalgene or other 32 oz. bottles, and only weigh 3.8 oz. each.

Hunersdorf Expedition cold weather water bottles fit nicely into the Bottle Boots (see photo). If you’re into mountaineering, a lot of professional guides require that you bring Hunnersdorf bottles on expeditions instead of Nalgene bottles because they’re less likely to crack in extremely cold weather. They’re also easier to open while wearing heavy mittens or gloves and at $9.00 each, they’re an inexpensive luxury. Weight wise, Hunersdorf bottles are also a lot lighter than wide mouth 32 oz. Nalgenes with loop tops, weighing 4.4 oz compared to 6.2 oz. That might not seem like a big weight difference, but you’re going to probably need 3 bottles for most trips and there’s no reason for you to carry more weight in winter than you have to.

If you’re into mountaineering or winter hiking, I encourage you to visit the Forty Below web site and check out Joel’s other products. His overboots, vapor barrier vest, and brewing products (yes, that’s right), are all state of the art and worth checking out if you want a winter warmer (can you spot the pun?), or a warmer winter.

Disclosure: The author owns this product and purchased it using their own funds.

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  1. I too have been using the Hunersdorff bottles for all my winter climbing. They work very well and I prefer them to Nalgene. I've also used the 40 Below Bottle boot but I don't love it. I;ve found the Granite Gear Aquatherm to work much better at keeping my liquids warm. The Aquatherm is more bulky but I’m willing to sacrifice a little bulk for better performance.

  2. Can you describe the difference in performance?

  3. Can you clarify what you mean by, "your body loses moisture much faster in cold weather"? Surely you can't mean "compared to hot weather."

  4. No, you lose significantly more water simply by breathing cold dry air in winter. Then there's the other complication which is you can't drink enough to replace it since you have to melt it first. This is why it's important to pre-hydrate in the morning and then drink a lot at night before bed so that you digestive system can break down the extra food you need to eat and carry waste products away from you muscles.

  5. The 40Below bottle boot is a compromise of weight, size and insulation. The 40Below boot works well for climbing high summits where you keep a one liter bottle in your parka. The streamlined design of the 40Below boot is perfect in this application. The Granite Gear Aquatherm is a bit larger and heavier but it has one significant advantage over the 40Below boot and that is insulation. The Aquatherm keeps liquid hotter longer as it uses half inch closed cell foam and a reflective film to radiate heat back into your bottle. I use a combination of both during winter. The 40Below boot is attached to my shoulder strap for easy quick access while climbing. The Aquatherms are in my pack keeping liquids nice and toasty.

  6. That makes sense and I might adopt something like that myself. I keep two 40 below boots bottles on my hip belt so that I carry them close to my hips and not in my pack. I like them specifically because they are so easy to deal with when wearing gloves or mitten because they close with velcro and not zips. But it would be nice to have a liter of water that is at warmer by the end of the day. Your combined system makes sense.

  7. The Aquatherm does not use zippers so it's easy to manipulate with gloves. It uses the popular pull string type closure with that little plastic lock that is seen on most packs.

  8. Just pointing out that there are two types of Nalgene bottles. Before the nowadays more common transparent, we had the classic white ones, which are still sold. This ultralight HDPE white plastic (now in other colors) are the same weight as the Hunersdorfs but much easier to find and cheaper. The material in these HDPE translucent bottles is also much more resistant to cold and heat than the transparent Nalgenes. I

  9. I just got a 1.5 liter Hunersdorf bottle but usually use my Nalgene with the lid loop so I can hang it off a carabiner on my pack. How do I hang my Hunersdorf bottle from a carabiner?? The “cord-around-the-neck” system never seems to work very well as the weight of the water causes the cord to pull up into the threads below the lid.

  10. Wait a minute, I found the solution. There are several little tab openings around the yellow lid which allow a cord to form a hang loop. Problem solved.

    • If you use a 40 below bottle boot, you hang it from the gear loop on the outside of the Neoprene insulation. But you probably don’t want to hang it from your hip belt with a tall 1.5 liter bottle because it’s bound to hit your knees when walking.

  11. Hello, bottle Kunersdorf without insulation keeps you warm water for a long time as a bottle nalgene. I use 32oz Nalgene that keeps hot water approximately four hours, finally naturally water is cool but not cold. How long retain hot water bottle Kunersdorf without insulation if you have an idea with isolation and how long time the water becomes cool?

  12. Hey Philip, Do you like it on your hipbelt? what do you think about being able to keep it on your shoulder strap? Also, do you like the way it straps to the pack? what would make this better? Also, how do you carry your water in the other months, warm temps?

    • Depends on the pack I use. I often attach it to a gear loop if my hip belt has one. Otherwise I stow a bottle and boot in the side pocket and stash my other ones in the pack next to my down jacket/pants. The rest of the year I just carry 2 x 1 liter plastic water bottles, reused. Two pounds of water on a shoulder strap? Don’t think so.

      • Gotcha…So if you don’t have the water on your hipbelt, do you usually stop and have someone else get your water out for you? or do you loosen/take off your pack to access water? I have seen a lot of PCT DIY water bottle holders on the shoulder strap, especially for a gatorade or smaller plastic water bottle.

        • I just reach back to my side pockets (I only use packs with side pockets) and pull my bottle out. When I’m done, I put it back in without taking my pack off. My guess is that those PCT hikers use shoulder strap bottles because they haven’t realized they could just cut them off. :-) [they come standard on ULA backpacks…popular on the PCT]

      • Having the bottle attached to the gear loop on hip doesn’t cause it to bounce around too much/interfere with leg movement?

  13. haha makes sense :) Thanks Philip!

  14. $34.95 each now for the 1L Bottle Boots (a 75% increase in price from $19.95 in 2019), but they’re still very much worth it. I replaced my Nalgene brand insulators which had zippers on them. They worked, but these FortyBelow ones are the real deal.

    • There’s a global neoprene shortage right now.

      • Plenty of inexpensive neoprene products on Amazon as of Nov 2023 for very competitive prices. No shortage of wine totes, booties, or wetsuits. And I found 1L Hunersdorf (Hünersdorff) bottles in Europe for €7.19, but no shipping to USA, so I have to accept that 40Below charges almost 3 times as much at $22.95. We all want to make a living but I’m struggling with 40Below’s pricing.

  15. Phil,

    I see Hyperlite now offers a bottle insulator. At $70 (hey it’s HMG) it might be a nice product for you to review.

    It uses zippers which I know some don’t like. I was using the Nalgene product with zippers without incident so not necessarily a deal breaker for me. They claim to use some thinsulate under that Dynema shell.

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