Standards Watch: Sleeping Bag Temperature Ratings

[Backpacking Light]

In this installment of Standards Watch, Rex Sanders tackles sleeping bag ratings: the standard, the pros, and the cons.

• Standards Watch: Sleeping Bag Temperature Ratings

[Cameron M]

Very interesting, thanks for the review Rex.

I have found that down thickness is one important parameter that is a fairly uniform indicator if there are no cold spots. Another big factor I have learned is important but more difficult to quantify in these standardized tests for both bags and jackets is how well the item fits; excess airspace inside the garment absolutely means less warmth.

[Jerry Adams]

Good info, you’ve covered pretty completely all the factors affecting actual temperature rating, thanks

Good links.  Another one is the Mammut Sleep Well document, for example https://www.scribd.com/document/156159764/Mammut-Sleep-Well-Pt1-E I couldn’t find it at mammut.com where it used to be

My complaint about the EN standard is it requires an expensive manikin test for each model of sleeping bag.  This is okay for a big manufacturer that sells many of each model, but is difficult for smaller manufacturers.

They ought to use a manikin test to come up with a way to calculate temperature rating based on thickness of sleeping bag and other factors.  It would come close to the EN rating without the expensive test, good for smaller manufacturers.  It would also make it easier to design sleeping bags, like, how much does a draft collar reduce temp rating vs how much weight and cost does it add.

 

[Eric Blumensaadt]

Thanks Rex. I know I’ll be referring back to your article when I upgrade my grandsons’ 3 season sleeping bags for the Sierra Nevada (what’s left of it).

My 3 season bag is a factory overstuffed Western Mountaineering Megalite now good to 20 F. instead of the original 30 F. This overstuffing happened after a chilly 26 F. night in a high valley below Olancha Peak on the PCT. REI FLASH Insulated R 3.7 mattress used.

My winter bag is an LL Bean -20 F. 750 fill “responsibly sourced” down bag that IS good to -20 F. (with heavy base layer and fleece balaclava). REI FLASH All Season R 5.3 mattress used.

So I know my sleeping bags’ actual temperature ratings and they are accurate – for me that is.

 

[Rex Sanders]

Thanks for the comments.

Cameron – If temperature ratings were easily correlated to down thickness or loft, life would be much simpler. Years ago, one bag maker published a chart with loft vs. temperature every year. Not any more. Many design details affect the measured, real, and perceived warmth of a sleeping bag.

“Airspace” is tricky. I’ve regretted trying to sleep in bags that were too slim for my comfort. The same ISO standard also covers sleeping bag dimension measurements and labelling, but those are rarely featured or discussed. Americans in particular come in a wide range of girths at the same height. Can’t design mass-market products just for (vanishing) skinnier people. WM is the only off-the-shelf maker I know of that still tries for some products.

Jerry – Yes, buying a manikin and building a test chamber is not cheap. But shipping a bag to Kansas State for a $600 test is reasonable. Still mystifies me that some bag makers chose not to test to the standard. Or some do and hide the results.

And small design details of fabrics, construction, drawstrings, collars, draft tubes, zippers, insulation distribution, etc. are why sleeping bags with identical loft perform differently. Hard to generalize.

Loft + features = rating would be easier to push for profit than independent testing – and much cheaper. Testing would quickly vanish.

— Rex

FYI: WM has EN-tested most of their bags – but buried the results here under the question “How accurate are Western Mountaineering temperature ratings? Do you use EN rating?” Their advertised numbers more-or-less split the difference between EN/ISO Limit and Comfort.

[Matt Dirksen]

Thanks for your summary, Rex. I was wondering about something you wrote:

“Before testing begins, a climate-controlled room is set up to meet the standard. The sleeping bag and manikin lie on an R 4.8 (RSI 0.85) pad….”

Given that the new ASTM F3340 effectively tweaked the R values for most sleeping pads on the market, is there any information on how ISO 23537 actually determines if a sleeping pad meets R 4.8 before it can be used in their test? Because some pads clearly lost some R value when F3340 came out, so whose to say the pads used in ISO 23537 are actually a different R value when tested through F3340?

[Rex Sanders]

Matt: The standard says the mattress must be 0.85 +/- 0.6 m2*K/W (R 4.8 +/- 0.1) “when tested in accordance with ISO 11092.” So ISO 23537 sleeping bag testers are supposed to use an ISO 11092 tested mattress. That’s a testing detail that I haven’t seen reported.

ISO 11092 is on my to do list, don’t know how it compares to ASTM F3340.

Most ISO standards rely on a bunch of other ISO standards, which rely on a bunch of other ISO standards, etc., each of which gets updates and amendments from time to time. ISO 23537 Part 1 references six other ISO standards, has it’s own amendment, and has a separately-published Part 2 that overlaps with Part 1, but not for temperature ratings. Quite the rabbit hole!

— Rex

[Rex Sanders]

Oops – should be “0.85 +/- 0.06 m2*K/W (R 4.8 +/- 0.3)” above.

Numbers and I usually get along fine. But sometimes …

— Rex

[Matt Dirksen]

Thanks for the clarification, Rex. While I got a copy of F3340 when it came out, I’m deftly curious what ISO11092 sets up for measuring R value on pads of varying construction.

It’ll be interesting to see how pads test on both ASTM to ISO.

On another note, the one thing that seems to be often left out of most conversations regarding sleeping bags is the impact of air infiltration due to movement of the sleeper.

In the architecture/building world, the old rule of thumb is the convective heat loss due to a square inch of an air gap in an exterior wall assembly is equivalent to the conductive heat loss of about eight square feet of no insulation. In other words, a very small air gap in a system can impact the overall thermal environment in a HUGE way.

There seem to be enough sleep studies out there nowadays which clearly point to people shifting positions many times per night, even in the most comfortable environments. Some types of bags (with good draft collars) may not ever show up on the tests as quantifiably better, even though they are generally proven in field use.

(In my opinion, this is similar to why air-only mattresses seem to “test better” than ccf pads, since the pads are only subjected to static pressure… and why most folks who hike in the winter always recommend to supplement an air mattress with a ccf pad.)

[Rex Sanders]

Many design details not measured by static testing can make a big difference in actual and perceived sleeping bag and quilt warmth.

A few decades ago, one sleeping bag maker made a big deal about adding a small, fixed triangular flap inside at the bottom of the zipper – sometimes called a zipper garage. This dramatically slowed air leakage that often led to cold feet. Most bags didn’t have that feature. When I switched, I discovered that a couple grams of fabric and thread make a big difference.

And neck-draft collars are standard or optional on most quilts now – for good reason.

“… high-quality gear reviews will continue to play an important role in sleeping bag and quilt selection.”

— Rex

[Author]

Posts