Western Mountaineering vs. Ray Jardine: Sleeping Bag Temperature Ratings

Nice loft measuring technique Stephen.  Doesn’t require expensive equipment.

That makes sense to just look at loft, although down has less temp diff per loft than synthetic.  If you over stuff the down the temperature difference per loft goes up…

The EN standard has never made sense to me.  Too expensive to measure each size of each model of sleeping bag.  Only large manufacturers can afford it.

They should use the EN standard to look at a range of sleeping bags and come up with a calculation of temperature rating based on quantities like loft and material.  Whether it’s a mummy bag.  etc.  Then it would be much easier for manufacturers to spec their gear more consistently.

It appears that Ryan is dividing the loft by 2.  In other words, half a sleeping bag. This is confirmed by the caption on his graph. However, his Y axis is the listed temperature rating.  Using the same data, my regression slope is half of his because I use the listed loft for the entire sleeping bag.  I don’t know why he did it that way, but you can address your question to him. Certainly, WM does not rate half a sleeping bag.  The measurement of loft for a sleeping bag is the whole bag.  Particularly for WM, where baffles are continuous, you cannot measure one side or the other because you don’t know whether the down is sitting in the top or bottom half of the bag. EE does rate its quilts using the loft of the flat blanket, not a sleeping bag configuration.  Their ratings for down, if doubled, are in the same ballpark as the numbers I derived from the WM data.  The loft for synthetics is not comparable to the down loft for these purposes.

Henry:  I have been doing some snooping in dusty corners of BPL.  As with most subjects, sleeping bag warmth by loft has come up many times.  Back around 2007, a BPL sleeping bag warmth table was created. I found a link to it, but the link goes nowhere.  Perhaps other readers know how to find it. It used half the published loft of the bag for plotting purposes. I presume, under the theory, that the bag user crushes the bottom loft, so only the top loft provides warmth. I am sure this has been debated somewhere:  a back sleeper will crush more bottom insulation than a side sleeper.  In any case, we get similar results once you divide Ryan’s results in half.  Our WM data sets are probably a little different.  I only included mummy shape bags for which WM also provided EN/ISO test results.  If Ryan included all products listed in the WM specification sheet, his results would vary a bit from mine.  My data was produced for a different purpose.

It appears that Ryan is dividing the loft by 2.

You are absolutely right. I did a little sleuthing and found WM’s data here: https://www.westernmountaineering.com/sleeping-bags/specification-chart/

When I divided the loft by 2 I get Ryan’s curve:

Since WM makes some quilts, I had to manually not divide the underquilt by two to align it with other data. Interestingly enough the overquilts did need to be divided by two (or they showed up as outliers). I think that is because WM overquilts are designed to fully encompass your body.

I also found EN ratings for a select number of WM sleeping bags in the FAQ’s: https://www.westernmountaineering.com/faqs/

and here it is for half loft:

It is interesting that the EN ratings have higher variability than WM reported values. That tells me WM primarily uses loft to rate their bags for temperature. You would expect higher variability in lab measured values. While that is the case they are still well correlated. It does not appear that the EN rating is a broken test.

Hi Henry:  Your last conclusion is the most important finding.  Now, take the average of EN comfort and limit and compare them with the WM rating for each bag with the available info.  You will be impressed by how consistent these generally are.  The rating convention used by the manufacturers use nice round numbers.  People look for a 20 degree bag.  Not a 17.  Take a look at the 7″ loft bags.  They show a bit of a rating range, but should not since the lofts are the same.  I asked them about this and they could explain the choices they made for the ratings based on bag features.  So, ratings are based primarily on loft but can vary a bit based on features.  As near as I can tell, the claim that the ratings are broken is based on a single case.  Sleeping bags are simple, yet, in some aspects, complex.  The fact that a sleeping bag test result surprises a manufacturer does not mean the test result is wrong.  It may mean that the bag needs more study to determine why a particular result was unexpected.

Enlightened Equipment uses a straight equation between loft and temperature rating (Temp Rating = 70°F – 20*Loft, r^2 = 1). Plotted on the graph above, their line sits between WM’s rating and the measure EN Limit rating for those bags.

Western mountaineering bags do not necessarly  have 1 uniform loft.  Around the chest /shoulders and around the feet can be much  loftier than middle body area. Just look at any photo of one laying flat. The loft across the chest maybe twice the average loft of the bag, the foot box too.

on a quilt it’s basically constant.

I always consider my EE quilts to be in reality about 10° worse than their rating.  My feet also get cold often in  quilts , they do not in a western mountaineering bag.

Wonder why? No, wearing down booties does not help.. it actually makes it worse.

My feet need to be kept warm by keeping the air in the bag warm…which the rest of my body does in a well insulated bag.

When the foot box is poorly insulated the area around the feet get cold, end of story. Cold feet. When it really gets cold I end up having to pull them up near the rest of my body and then the foot of the quilt turns into an ice box and I can’t put them back down there for the rest of the night.

Moral of the story for me, is Western mountaineering knows what it’s doing. It knows where to put the most loft in a bag to maintain warmth.

EE was known to be very optimistic on their temperature ratings, many people complained about it.

Supposedly they changed to a more accurate rating system recently, but I haven’t used a new one.

Also EE had habit of putting the most insulation in the tubes on the side of you…. You know the ones that lay on the ground….. and very little on top…….. It’s almost like they fill the tubes on top last and stopped when they got to a certain weight….. Leaving those…. most important ones

… under filled

I added 1.5 oz of down to an ee quilt years ago and I would still rate it 10° off of its as- sold rating.   Part of that is poor performance of 950 down in real conditions.

In terms of cold feet in EE, I have an early Revelation and I cannot get the footbox to close up enough on cold nights to not feel a heat leak. I’ve bought an Enigma more recently and like it much more. I also bought my Revelation with an extra ounce of overfill and feel like it could have used a bit more. IIRC so many people were buying more overfill he started putting more fill in the quilts. I think this data shows that 20°F/in rating is a bit aggressive in reality. It shows up in the WM bag data and I can’t imagine quilts do any better at cold temperatures. I also think this data shows loft is the overarching driver for temperature ratings. It sure would be nice if more companies would give you the data. Of course, quantifiable data is the enemy of marketing :(

This got me thinking about other manufactures. Here is the data I could find:

Jacks R Better and Zenbivy did not report loft (that I could find). Zpacks uses the exact same equation that EE uses (70 – 20*loft). Katabatic appears to have the most conservative rating (63.6 – 15*loft).

——–

I have a new 10°  with 850 down that I got on Black Friday because it was pretty good deal.     Going to test it out tonight in my backyard because it’s going to be 18F.  Hoping this turns out to be a true 20° quilt for me.  I was colder last spring several nights than I wanted to be in the mid-20s.  I think I’m also getting colder as I get older.

Kind of bummed, they were calling for a few degrees cooler just a couple of days ago.  I was hoping for 15 f.

Temperature supposed to fall all night so it’s not going to get really cold till dawn so it’s not a great test.   Tomorrow evening will be about the same and it’ll never get above freezing tomorrow so tomorrow night will be a little better test….colder longer

Ultimately, it’s how warm you feel in a bag; not the ratings.

As has been discussed a gazillion times, one person will be cold in a 30 degree bag on a 40 degree night… another person will be warm in that same 30 degree bag on a 10 F night…

Thanks for the graphics, Ben H. Clipped and saved! I plan to carry these in my backpack to remind me that I *should not* be cold in my EE RevX at 25F, since it can loft to 3 inches!

If all manufacturers rated their bags the same, it would be easier to compare to select which one was best for you

If you determined that you were warm, for example, 10 degrees colder than the rating on one bag, then you could assume the when selecting a new bag and just add it to any other rating.  Probably close enough

If all manufacturers rated their bags the same,
Hilarious!
Totally the opposite of what every marketing department wants. Quote: ‘Of course OUR bags are far superior to everyone else’s.’

You can’t have facts intruding into the American world of marketing spin. Curiously, the Europeans are very much in favour of rigorous testing to a published Standard. Why the difference? I do not know.

Cheers