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Your Lowest Temperature with a 40F/4C Bag
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Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Your Lowest Temperature with a 40F/4C Bag on 11/18/2008 14:08:32 MST Print View

I have a 40F Degree Marmot Atom bag and I am curious to see how cold of a temperature that I can reasonably use it at.

What was the lowest temperature that you were able to comfortably use your 40F/4C Sleeping bag at?

Please let me know the following:

1. Sleeping bag you used
2. Sleeping pad(s) you used
3. Shelter you were in
4. Clothing you wore to bed

For myself I have the following:

1. Marmot 40F/4C Sleeping Bag (1 lb)
2. GG Torso Pad & Thinlight full length pad
3. MLD eVent Soul Side Zip Bivy
4. BPL Merino Wool Long Johns & Long Sleeve shirt, REI wicking shirt, OR wind shirt, Montbell Thermawrap Jacket, REI convertable pants, light fleece hat, light gloves.

Thanks for your input....curious to see what people have achieved.


Chad Miller

Locale: Duluth, Minnesota
A 40F bag is good down to . . . on 11/18/2008 14:14:20 MST Print View

Well lets see. . .

40 degree quilt from Jack’s R Better
prolight 3 short sleeping pad
midweight ploypro long top and bottom
fleece hat
hiking socks

. . .and surprise, surprise the bag was good to 39-42 degrees.

Matt Lutz
(citystuckhiker) - F

Locale: Midwest
Similar discussion on 11/18/2008 14:16:15 MST Print View

Here's a similar discussion in regard to a 30 degree bag, a Marmot Hydrogen.

Jay Wilkerson
(Creachen) - MLife

Locale: East Bay
40F Bag on 11/18/2008 14:35:21 MST Print View

Hey Tony, I have WM Linelite and it is rated to 45F= 15.1oz
Thermarest 72 x 1.5 = 24oz
GG Spinntwinn with MLD Serenity Shelter = 19.9oz
Patagonia LJ, Patagonia LS, WM Flight Vest, Nike beanie and REI sox = about 20oz.
I have taken that combo on a lot of hikes and have slept in high mountain passes and next to lakes in June,July Aug. and have never been uncomfortable. I change to a WM 20F in Sept. in the Sierras. See ya at Pt. Reyes.

Edited by Creachen on 11/18/2008 14:39:32 MST.

Mark Verber
(verber) - MLife

Locale: San Francisco Bay Area
Re: Your Lowest Temperature with a 40F/4C Bag on 11/18/2008 17:50:16 MST Print View

It would be best to avoid talking about a manufacturer's "stated" rating. Ideally you should compare using the EN 13537 standard, or at least compare loft of the bag. The For the record, it looks like the Atom is rated as a 50F cold sleepers, and 43F for warm sleepers.


Jamie Shortt
(jshortt) - MLife

Locale: North Carolina
Your Lowest Temperature with a 40F/4C Bag on 11/18/2008 18:54:33 MST Print View

Tony, I'm going to estimate you should be able to take your Marmot atom setup down to 25 degrees and still be comfortable. This assumes you are an average sleeper with respect to temps. I'm basing this on my experiences with my Marmot Hydrogen which I believe can go to 10 degrees even though its rated to 30 using a setup almost exactly like bivy, ground insulation, and clothing options are nearly identical to yours.

Weekend before last a friend and I were on Mt Mitchell, NC camping at 5500 feet and the low temp for the night hit exactly 20 degrees. My friend was using my Hydrogen sleeping bag on a trimmed ridge rest and inside a Montbelll dry-tech bivy under a golite poncho tarp. His insulative clothing was a wool cap and fleece jacket. I was sleeping in a Golite Ultra 20 quilt on a GG thinlight (trimmed 42" long by 3/8" thick)inside a MLD Superlight Bivy under a Integral Designs Silponcho. I had a fleece cap, but added my Montbell Down UL jacket during the night. At times the wind had strong gusts. We both woke up fine despite being exhausted and going to bed relatively cold. I'm guessing we could have managed a drop of another 10 degrees. I honestly think the 30 hydrogen can be used in lower temps then the 20 Golite Ultra. But the Ultra weighs under 19 oz so it is still amazing item.

Because of this I would think you could extend you Atom similarly...reason why I'm suggesting 25 degrees.


Mary D
(hikinggranny) - MLife
Your Lowest Temperature with a 40F/4C Bag on 11/19/2008 15:30:27 MST Print View

As mentioned, the manufacturer's temperature rating means very little, and it's best to check the EU ratings, if the bag is sold in Europe as well as the US.

My own experience with a Marmot Hydrogen (30* F), is that I started having to add clothing layers in the upper 30's. On a 26* night, with all my outer clothing (even rain gear) on inside the bag, I still was shivering. Clothing included midweight base layer (REI MTS) top and bottoms, nylon hiking shirt and pants, 200 weight fleece jacket with hood, fleece cap, polypro glove liners, frogg toggs jacket and pants (with hood on), heavy acrylic hiking socks. Sleeping pad was a Thermarest LE. Where I was coldest was on my hips, even though the sleeping bag was not stretched tight (I checked). The dog slept at my feet, so they stayed warm. I slept on and off, but kept waking up shivering. I needed two more dogs--one on each side of my hips!

Last August, with temps down to 20*F, I was fine in my Western Mountaineering Ultralight Super bag, with base layer plus nonbreathable rain gear (Brawny Gear rain jacket and pants, now sold by BPL) as a vapor barrier liner. I also wore a polypro fleece balaclava and a pair of 200-weight fleece socks (much more comfortable than hiking socks). The draft collar in the WM bag really made the difference--once I snugged that around my shoulders, I was just fine.

Both nights were windless, BTW, and I was in a single-wall, well-ventilated shelter both nights.

Obviously, I'm a cold sleeper. If you are one also, don't plan to get that 40* bag below the mid-30's.

Edited by hikinggranny on 11/19/2008 15:36:37 MST.

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Re: Your Lowest Temperature with a 40F/4C Bag on 11/19/2008 16:07:27 MST Print View

I would like to say thanks to everyone for their input.

I am a cold sleepers, so I am guessing that I might be able to push the Atom down into the mid 30's maybe 32 degrees.

I also have the Marmot Helium EQ, which is rated down to 15 degrees F and I have taken that down to 5 degrees F wearing a ton of clothing and was fine...except my head, which needed two caps vs. a light fleece hat only.

The kicker is that the Helium EQ is 2 lbs 3 oz.....I find it difficult for me to consider spending more money on another sleeping bag...say the Hydrogen at 1 lb 8 oz....when for 11 oz more than that, I know that I am good down to 15 degrees or lower.

Forget that my wife might kill me if I bought ANOTHER sleeping bag....heck, I might kill myself for having another sleeping bag. :)

I have 3 being a 20 degee synth bag that is over 3 bag pre-BPL and my light weight sickness.


Mary D
(hikinggranny) - MLife
Your Lowest Temperature with a 40F/4C Bag on 11/20/2008 00:19:19 MST Print View

OK, you have the cold bag and the warm bag, and you've identified yourself as a cold sleeper. I wouldn't bother getting the Hydrogen because the two bags you have can overlap very nicely.

Since the Helium EQ has, I understand, a full-length zipper, you can use it on warmer nights by ventilating. This was more difficult with the older Helium which had only a 3/4 length zipper. I do this with my 20* WM bag. I have been known to lie on top of my bag for a while until it cools off enough to get inside.

I would take the Atom for warmer weather (you can wear outer clothing inside if it gets unseasonably cold, and get down to freezing or close to it). For spring and fall, or if you're going someplace like the Rockies, where it can get below freezing or snow anytime, I'd take the Helium.

Your mileage may vary, but try each of these combos out and see how it goes. At least on the west coast, the next few months are a great time of year to try gear out in the back yard to see how you fare in inclement weather.

Roleigh Martin
(marti124) - MLife

Locale: Moderator-JohnMuirTrail Yahoo Group
Re: Your Lowest Temperature with a 40F/4C Bag on 11/20/2008 07:30:56 MST Print View

How much warmth does the MLD eVent Soul Side Zip Bivy add to sleeping? Would it make one feel that a 32 F Western Mountaineering bag is more like a 20 F WEstern Mountaineering bag?

I did the JMT in 2008 from last week of July to mid-August and used a WM Flight jacket inside my sleeping bag to keep my upper body warm during middle of night but my legs got a little cold. I'm curious what the Bivy would do for it.

I sleep in a tarp tent and it has so much ventilation it is almost like sleeping under a tarp.

Kevin Landolt
FF Vireo in Wind River Blizzard on 11/20/2008 09:06:58 MST Print View

Gear: Feathered Friends Vireo (72 inch version, rated to 45 degrees)Patagonia R1 Pullover and Patagonia Down Sweater

Inside a BD Megalight...

Situation: Wind River Mountaineering Trip, two days of wind and rain and below freezing nights lead to three days of high winds, two feet of snow falling, and two nights where the temp fell below -10.

So already wet from traveling and camping above tree-line in wet windy conditions, the blizzard really pushed my system to it's limits. As frozen condensation rained and melted on me constantly. Hot water-bottles and push-ups/sit-ups kept me functioning and surprisingly in high moral!

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Re: Re: Your Lowest Temperature with a 40F/4C Bag on 11/20/2008 10:37:01 MST Print View


This year I made the switch from using my beloved Contrail Tarptent to a MLD Bivy & Poncho Tarp.

I would conservatively say that the bivy adds 5 degrees F to as much as 8 Degrees F to the warmth of my bag and "feels" much warmer than my tarptent.

The bivy traps more heat than a tarptent, but with the possibility of having condensation inside the bivy.

I have an eVent top on mine and rarely have I had condensation issues.

There is a very generous amount of netting on my bivy to let the moisture from my breath escape the bivy.

For me, the biggest issue was to get my headspace adjusted to the confines of the bivy.

I happen to have a wide version of the MLD Soul Side Zip, so I have plenty of room to sleep on my side, roll over, and I have a ton of space above my head to put my shoes, ditty bag, Montbell Thermawrap jacket, etc. (I am 5' 6").

The only reason that I have my 40F Degree Atom bag is because I have a bivy, as I am a cold sleeper.

If I knew that I was going on a trip where lots of rain was a possibility, I would probably take my Contrail for the extra room. The thought of being "trapped" for hours in my bivy in a storm under a tarp does not sound all that appealing, but I am a newbie at the whole tarp thing.

If you want to see a photo of my Poncho Tarp & Bivy setup, go to the photo gallery and see the Emigrant Wilderness entry. There is also a photo of the MLD Superlight Bivy too, which my friend, Jeremy uses.

Hope that this helps you, if you are deciding to make the switch to a bivy & tarp.

P.S. Mary...thank you for your input. You seem to confirm what I was thinking, stick with what I have...the Hydrogen would be overlapping my two bags.


Edited by Valshar on 11/20/2008 10:40:58 MST.

Rick Dreher
(halfturbo) - MLife

Locale: Northernish California
Re: Your Lowest Temperature with a 40F/4C Bag on 11/20/2008 11:12:35 MST Print View

Buy an FF Wren and tell her it's a really long jacket?


Tony, I've accumulated more bags than you (yes, it's a sickness of some sort) and most can take me past the low rating, given the right environmental variables, good nutrition, lack of exhaustion and dry clothing. Most have also failed to keep me comfortably warm due to one or more of those elements being out of whack.

If your bag is sufficiently roomy to accommodate extra clothing (I don't know how snug that bag is) I can't think of a reason why it won't take you to freezing and beyond with extra clothing, in the bivy sack and under the cover of a shelter--be it tarp or enclosed tent. It's also very important to pick the right campsite to take advantage of warmer microclimates in the area. Frankly this last bit takes experience and a lot of lucky guesswork.

And take care of yourself. Be well-fed and dry when you hit the rack, and you'll always sleep better. Again, sometimes it doesn't work out that way, but if hiking in foul weather it's often better to stop before the day's goal to pick a better campsite and allow enough time to dry out and eat a proper dinner.

That's enough rambling from me.

Jamie Shortt
(jshortt) - MLife

Locale: North Carolina
Your Lowest Temperature with a 40F/4C Bag on 11/20/2008 17:25:18 MST Print View

Roleigh, I've found that a bivy really extends my temperature rating. That and a fleece cap. My thought is a bivy under a tarp is good for about 10 extra degrees. This is why I placed Tony's Atom + Bivy + Thermal Warp + Cap + Gloves at 25 degrees and still be comfortable. Probably not toasty, but still fine. The more windier the more a bivy helps as well. I've been really amazed at the temps my Hydrogen supports with a bivy as well as my Montbell thermal sheet (14.5 oz full zip quilt).