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Cozies: Are they worth the weight?
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David Poston
(dgposton) - F

Locale: Texas / Colorado
Cozies: Are they worth the weight? on 07/13/2013 15:11:05 MDT Print View

Has anybody done testing with cozies to see if they are really worth it? Certainly they keep your food a bit warmer, but do they help significantly with the rehydration process? My MYOG envelope cozy (made from reflectix) weighs in at 1.45 oz. I'm wondering if it would be worthwhile to bring one for my pot as well, or just bring the lid (or not). I use an Al foil lid which weighs in at 1.54 g.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Engineering calcs on a Saturday afternoon. on 07/13/2013 15:57:04 MDT Print View

Short answer: Your aluminum foil lid is the highest, best ROW (return on weight), followed by (other pot attributes being equal) heat exchanger fins on your pot, and lastly, a cozy.

Long answer: For the cozy, it depends on your cooking habits and trip length. But as an example, I'll make some assumptions and do the calculations:

1 liter pot, 0.5 square feet of surface area on the sides.

Delta T between pot temp and ambient air: 190F (average of 170 to 212) minus, say, 50F = 140F

R-value of air film with no cozy: 1

R-value of cozy plus air film: 2.5

Conductive/convective heat losses to the air: 0.5 sq ft x 140 F x 1 (BTU/hour-sq ft - F) = 70 BTU/hour heat loss.

Two meals a day, hot drink and hot entree in each, two weeks, 10 minutes heating and eating each of the four hot items each day: 4/day x 10 minutes each x 14 days = 9 hours.

So 630 BTUs saved. butane, propane and white gas are about 20,000 BTU per pound (but a HX pot is about 50% efficient, so you only get 10,000 BTU per pound of fuel) so 1 ounce of fuel is saved by using the cozy.

Without showing all the details for radiant heat loss, I estimated the cozy outer temp at 106F versus the bare pot at 190F. The difference in heat loss (153 BTU/hr off the bare sides versus 88 BTU/hour off the cozy) gives a savings another 585 BTU over 9 hours or one more ounce of fuel for a total of 2 ounces of fuel saved (conduction plus radiant).

Bottom line: You'd need to be be doing a fair bit of cooking over a two week period to come out ahead, balancing the weight of the cozy to the weight of the saved fuel.

However, not burning your hands on your morning coffee and oatmeal probably has some value. One pot of Ramen dumped onto to the ground because you were burning your fingers, and that represents weight and time. If you didn't have a cozy, would you use a pot gripper? I've made a 9 grams pot gripper, but most commercial ones weigh more.

Stephen M
(stephenm) - MLife

Locale: The Deep Frreze
Re: Cozies: Are they worth the weight? on 07/13/2013 15:58:52 MDT Print View


I do think a cosy helps a lot, especially when the weather is cooler.

I was on a trip last week where a buddy was cooking rice, rather than simmer it after bringing it to the boil I told him to put the
Pot in to my cosy and it cooked away inside it.

In winter I keep my gas cans and food I don't want to freeze inside the cosy.

Edited by stephenm on 07/13/2013 15:59:36 MDT.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Cozies: Are they worth the weight? on 07/13/2013 17:16:30 MDT Print View

I tried a cozy on a few trips. "cooking" oatmeal or dried soup didn't really matter. Without a cozy, it cools down after a while, but before it cools too much it gets rehydrated.

If I was "cooking" food that was more difficult to rehydrate that didn't properly rehydrate without cozy, it would make a difference. So, if your food doesn't really get rehydrated enough, try a cozy, and if it's enough better then it's worth it.

If I want to keep something from freezing, or if I want to keep food or water cool in hot weather, better to position in middle of pack. If you use David's numbers, cozy gives you 2.5 R. Insulation in pack is maybe 4 R per inch, and it's maybe 4 inches thick all the way around, so it's 16 R - a cozy gives you insignificant insulation in comparison.

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Re: Cozies: Are they worth the weight? on 07/13/2013 17:31:56 MDT Print View

A cozy is great for holding a freezer bag of hot food in your hand and eating from it.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Cozies: Are they worth the weight? on 07/13/2013 17:57:36 MDT Print View

>"Insulation in pack is maybe 4 R per inch, and it's maybe 4 inches thick all the way around, so it's 16 R - a cozy gives you insignificant insulation in comparison."

Jerry: very true. Clothing makes GREAT insulation (duh). I'll move a few pounds of frozen fish thousands of miles wrapped in multiple layers of clothing interspaced with plastic bags to reduce air flow and water vapor migration.

Clarification: my value of R = 2.5 included the air film on the outside. I figured the cozy on its own as mo more than R = 1.5.

You say cozy. I say spare sock.

Mike Farrell

Locale: C.A
Cool cozy on 07/13/2013 18:04:03 MDT Print View

I think they are worth the weight. This one is worth the weight just for the cool factor of the flame job.
Sarbar cozy

Jeffs Eleven
(WoodenWizard) - F

Locale: Greater Mt Tabor
Re: Cool cozy on 07/13/2013 18:45:46 MDT Print View

One ounce?


Yes they work, so for one ounce... To have your whole meal be hot, not just the under cooked first five bites...

Yes. Its is worth it.

Unless, of course, you don't like hot food in cold weather.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Cozies: Are they worth the weight? on 07/13/2013 19:14:39 MDT Print View

> You say cozy. I say spare sock.
I say Australian bush hat.

As for the idea that without a cozy your dinner will get cold too fast ... we have never experienced that. Burnt lips a few times though.


Jim Colten
(jcolten) - M

Locale: MN
Re: Cozies: Are they worth the weight? on 07/13/2013 19:57:40 MDT Print View

Not applicable to UL hiking but ...

When cooking (not freezer bag cooking) for a group of more than a couple, a cozy covering the top and all but the lower inch or so of the pot yields very large fuel savings. Also cooking time savings. That can be a critical difference on long trips without resupply options.

cozy on 07/13/2013 20:45:47 MDT Print View

Yes , a cozy works good .

But for freezer bags, you dont need a dedicated cozy.

Use clothing, fleece, beanie, or even your sleeping bag. or sleeping pad. If you are scared of leaks, use another light flimsy ziplock and double bag it.

Hold the hot freezer bag in a bandana to eat.

no need for a 1oz cozy.

Edited by livingontheroad on 07/13/2013 20:47:17 MDT.

Paul Ashton
(PDA123) - F

Locale: Eastern Mass
Empirical on 07/14/2013 06:21:33 MDT Print View

Shows delta T for different levels. The main point is usefulness for cooking, not just boiling and rehydrating.