Montbell stretch bags

[Russell Swanson]

Need some info on the Montbell stretch bag temp ratings. They have two temps listed, the ‘comfort temp’ and ‘usable temp’. Wearing a lightweight base layer, just how uncomfortable is the ‘usable temp’? For instance, the usable temp on the #4 is 21 degrees but if it drops below freezing, are you typically shivering your butt off or in need of donning further insulatory clothing?

[Dondo .]

I have the synthetic #4 and am fine to the mid-thirties F. Below that I slip on a puffy jacket.

[Rick Dreher]

I’ve got an older model #5 and find the “comfortable” to be the minimum and imagine the “usable” would mean “no sleep.”

They’ve since altered the design and upgraded their down, so it could be that the bags are warmer now. The stretchy feature’s really nice.

[EndoftheTrail]

I own two MB down bags, and I find their “comfy” ratings to be spot on — meaning that when temps fall to the specified level, the bags no longer feel so toasty warm, but are still warm enough for me to fall asleep. I consider myself a pretty average sleeper. I sleep in silk long underwear, and I do not use any kind of liners.

Given the very wide range between “comfy” and “usable” ratings, I seriously doubt I would feel comfortable at the lower “usable” rating — and have no intention of trying.

[Richard Nisley]

The evaluations of sleeping bag warmth would have significantly more value if the posters specified the R-value of the mat they used to make their evaluation. Up to 1/2 of the body heat is lost through the bag’s compressed bottom and mat combination.

Secondarily the poster’s basal metabolic rate and body surface area will impact their experience. Their age, weight, height, gender, and other factors should be input to a BMR calculator and this value should be specified. This protects the source information which is more personal in nature. You can Google BMR calculator to determine this value.

[Dondo .]

Good idea, Richard. I appreciate you bringing a more scientific approach to the discussion. My BMR is 1518 and the mat I mostly use has a R-value of 2.6. My evaluations were done while sleeping under a shaped tarp or tarp-tent. I sleep a lot warmer in a small double walled tent.

[Dan Schmidt]

All the more reason to suck it up and
carry an inflatable pad, you gain comfort and perhaps break even in weight.

[Brian James]

I’d like to see a dummy-based testing system devised. A dummy with the conductivity characteristics of a human should be heated to human body temperature, and then placed in the bag at the bag’s rated temperature. The temperature falloff could then be graphed as a function of time.

I think that any publication that tested in this manner would be miles ahead of the pack in terms of bag testing.

[Joseph Rothstein]

I think that’s the approach used for the EN 13537 standard that’s used for sleeping bag temperature ratings in Europe.

[Richard Nisley]

Joseph

The going rate for a certified lab to test just the temperatures using the EN13537 dummy ranges between $577 and $1,218.

A complete EN13537 test sequence costs approximately $1,925.

[Brett .]

Russell, first of all; I recommend any current super stretch (Ultra Light) down bag; they are the most comfortable and versitile bags I have used; due primarily to the patented super stretch system no one else can legally copy. The inner baffle eliminates dead space and holds the inner boundary close; and the outer baffle stretches as needed to 75.6″(long bag) at the hips. I can actually sit upright crosslegged in my bags. I will never go back to a fixed-diameter mummy bag again. The temperature ratings are spot on for me. (Richard had a great way to compare; I’m BMR 1500, with an R2.3 mat; use a double wall tent). My #7 is (as advertised) a 50’F bag wearing a poly tshirt and boxers. I can add capilene1, a goretex bivy and/or Thermawrap as needed down to 40’F. Forcasts below 40 I take my UL #3 SS which is basically a 32’F bag. I trust that rating, but never been out below freezing. A #3 and #7, clothing and bivy provide a versitile system for any situation I expect. Let us know if you like the super stretch system?

[Russell Swanson]

“The evaluations of sleeping bag warmth would have significantly more value if the posters specified the R-value of the mat they used to make their evaluation. Up to 1/2 of the body heat is lost through the bag’s compressed bottom and mat combination.”

Richard,

I’m looking for a general trend of MB bag owners’ evaluations of the company’s claims. But, to be more specific, my BMR is right about 2000 and I use a POE Max Thermo. I’m not sure of the R value but I’ve used it in temps below freezing coupled with a a 20 degree bag and experienced no noticeable discomfort. I will use whatever insulation is neccessary to take care of that part of the equation, I just don’t want to buy a MB bag thinking I can get away with the minimum usable temperature listed and be dissapointed or worse. It seems that this ‘usable’ comfort rating is a bit ambiguous.

[EndoftheTrail]

Russell:

The usable temp is downright seductive… but again, don’t count on it being anywhere near comfortable.

IMO, rather than ‘wishing it were so’ — I suggest that you pick your MB bag based on the “comfortable” rating. This way, should actual temperature ever fall below expectation, the “usable” temp rating can serve as “insurance” — meaning that you likely won’t be comfy, but at least you will make it through the night OK.

[Dondo .]

Russell, I’d go along with Ben on this one. Even the sales people in the Boulder Montbell store will tell you to go with the upper rating. Go with the ‘usuable’ rating and you may well freeze your tuckus off.

[Dondo .]

Brian, I’m a big fan of the EN13537 system used in Europe. But Richard brings up it’s most serious flaw. The cost of the tests could well freeze out some of the smaller players and give a competitive advantage to the big boys. Dr. Elizabeth McCullough at Kansas State has been trying to get something similar going in the US but without much apparent success. For now, you can find EN test ratings for The North Face and Marmot and some of the European brands at their European sites.

[Mitchell Keil]

I wrote a lenghty review of the MB #4 a while back which you can find under the reader reveiw section. As many have pointed out MB gives you a range of temps from comfotable 8 hours sleep to just close your eyes and hope the night passes quickly “usable”. So much depends on your sleep habits, weather, energy levels, pad and shelter choices that all of our comments might give you no real help. IMHO MB bags are about as accurate as any Manufacturer when you are looking at the comfortable temp of a bag. Pack sleep clothes or wear what you have if it gets colder, but always use a bag that will meet the coldest temp you are likely to encounter as a starter or make sure that the extra clothes you carry will meet that criteria. I usually carry my MB ultra light down jacket and down pants and have been able to sleep comfortably to 25 with my #4. I also have a #2 and have had it down to 15 with the same sleep outfit. I will say that the MB stretch bags are the most comfortable bags I have ever slept in. Good Luck!

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