EN 13537 temp rating

6:42 a.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts

Here is an article about the EN 13537 norm. Some aspect will not be discuss as they are discussed elsewhere (see for example Mammut sleep well report).

I'll just discuss technical aspects and try to describe as precisely as possible how the get the temperature rating.

First let start with some physiology :

The EN test make some hypothesis about human physiology. The most important one for the test is the Heat production. The hypothesis is the following : a average man produce 38 watt per meter square of heat while sleeping. It's about 57 watt.

The model behind the limit confort temp  (actually it is the same model fot other temp rating, only parameters are changing):

 T_c=T_0-P*R

-T_c : is the limit confort temparature,

-T_0 : is the temperature at which an average man can sleep naked without any insulation. It is supposed to be 34 celsius (93.2 F) in the EN test. And it depends only on the physiology of the subject

-P : is the power output by meter square and depends only on the physiology of the subject. As I said it is supposed to be 38 in the EN test.

-R : is the thermal resistance which is related to dry heat loss (convection, conduction and radiative heat transfer. It doesn't take perspiration into account. So people that sweat more are forgotten in this number. It depends on the insulator as well as outer and inner shell. This number measure the insulating property of the sleeping bag. And is what Lab tester measure.

So a word about this model : If R=0 (no insulation) it gives T_c=T_0 which is logical. 

T_0 and P are strongly dependant on the individual. You can measure your own P and T_0 and determine what is your confort limit temperature quite easily. I'll make a post about that later. 

Now i rewrite the rule using the parameter in SI unit :

T_c=34-38*R.

I deduced this law in the following way. First T_c=T_0-R*P was the only formula that I could think of. I thought also about a quadratic correction term but by ploting EN test result on a graph I directly noticed it was linear. Then it was easy to determine the power output hypothesis. Then I compare the plot of this linear equation and compare with observed values and it fits perfectly. 

6:51 a.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts
EN 13537 Test : the settup

During the test, the tester place a copper mannikin inside the sleeping bag. He is dressed with long underwear as well as baclava or a hat. The exact clothing is not really specified. Then the sleeping bag is placed on a foam pad. His R-value is not specified and each lab can use what he wants. The pad sits on a elevated wood board. It has been shown that the thickness of the board as no influence on the results.

On the mannikin there's at least 20 sensors, (35 for some labs). The temperature is chosen by the tester and is not really relevant for the model used. The Thelma institute i Norway vary the temp according to the bag but IFTH in france don't. The humidity is kept constant and ranges between 40 and 80 pc. And the wind is 0.35m/s. 

The skin  temperature off the manninkin is kept at a temp of 34 degrees which is logical because it is supposed to be the confort temp of an average man sleeping naked.

As you noticed there's a lot of unspecified variable. The clothe, more importantly the pad and even the type of manninkin is not specified. The pad can make a huge difference. 

7:12 a.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts
EN 13537 Test : the test

Now that everything is settled. The tester can deduce the total R-value (thermal insulation). It does it in the following way :

The sensor measure the power output produce to keep the skin temp at 34 celsius (93.2 F) for that segment. Actually the measure the power per meter square. To get the R-value for that segment one just invert the value. So if P_0 is the power output for the head, 1/P_0 is its R-value. 

Now that the tester knows the R-value for each segment. He will proceed to a weighted averaging and get the total R-Value. The weight depends on the surface of the segment.

If you don't understand what's a weighted average. Let me give you and example.

Suppose we have only 3 sensors. One for the chest and one for each hand. Suppose that their respective R-values are 1 (chest) 0.5 (each end). Now because the chest is much larger I will give him a weight related to its surfaces.

Let say that the chest is 5 times bigger. its weight will be 5. The hand weight being 1. So instead of averaging as usual :

(1+0.5+0.5)/3=0.666

i'll will average but taking the surfaces factor into account so 

(1*5+0.5*1+0.5*1)/(5+1+1)=6/7.

If you still don't understand, let say that the bigger the surface of the segment the more it will be taken into account in the total R-value.

What is important is that I noticed that the weight only depend on the area of the segment and not on physiological considerations. For example the leg have a big area but are physiologicaly less important for survival that the head. This king of thing aren't adressed in the test. I may be wrong though as I didn't see how they choose the weight factor. I just have them with no explanation.

I tried to get the EN 13537 test technical details but it cost 70 US Dollars (50 euros). So i prefer to stay ignorant. I could find many things by myself without spending a penny.

7:25 a.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts
The problem with the EN 13537 norm

From what I learn I don't really trust this norm. The reasons are the following :

-unspecified parameter (clothes, pad, manninkin). The pad issue is the worst. I could check completely unconsistant result concerning the back insulation. It seems that the dorsal insulation are not related to the sleeping bag. As the area of this part is quite big it makes the test a little bit senseless as the error can be apparenty as high as 8 or 10F (5celsius).

-Even if the test are conducted in the same labs, the discrepancy between results are quite high. You can chech that on marmot website :

T_c of the Lithium : 6.1 F

T_c of the Lithium membrane : 0.3 F,

Then you can say well the 6F difference is coming from the membrane. It is more insulating. and then you chech the Never summer :

T_c of the never summer : 2.5F

T_c of the never summer membrane : 8.1 F

See it is completely illogical.  So you have an error ±6F in the same lab ±8F between labs. An error of 14F hum.

-The test doesn't take heat loss due to persipation into account. This can be easily solved using a VBL I guess.

-As I explained, it doesn't seem that the human physiology issue is properly adress. 

-Finally, the manninkin is still. If you move you produce heat. So a tight sleeping bag will perform better during the test than a larger bag. In the field if you move a lot during your sleep, you'll produce more heat and your larger bag may perform better. 

7:40 a.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts
Conclusion

What is the conclusion of all this. To me the answer is clear. I don't trust this rating. It's a step forward but there is too many problems. So I prefer to ask experienced people. If you are a novice and you want to buy a expensive mountaineering or winter camping sleeping bag, you better to rent one first to see what kind of bag you need or borrow one from someone.

If you're still not sure or really want to buy one i would recommend the following :

-think in terms of sleeping system instead of sleeping bag alone. Ground insulation is as important as your sleeping bag. Conductive heat loss is more important than convective heat loss. 

-For really cold weather always take a large fit sleeping bag. The reason being that you can add clothes without compressing the insulation of the bag, and bring some extra insulation. Specially for the feet and the head (I noticed that the chest area is always overinsulated. Its R-value is twice as big as the total R-value of the bag).

-Check the next post. it's a funny way to determine your own T_c for a sleeping bag. 

8:14 a.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts
Funny experience.

here is a funny experience to determine your own T_c for a sleeping bag.  You need to know the R-value of the bag or its limit confort temp rating following the EN-norm.

To get the R-value of the bag using the T_c (in celsius) of the bag, use the following formula :

R=(34-T_c)/38.

first step : determine T_0 (in celsius) which is the minimum temperature at which you sleep naked comfortably. Go in your bad or on the pad you will use with the bag naked and check the temperature.

second step : determine T_1(in celsius) which is the minimum temperature at which you sleep comfortably with a t-shirt and a short.

Third step : Now you can deduce your power output  :

P=(T_0-T_1)/0.077.

Now that you have your T_0 and your P you can determine the limit confort temp rating of the sleeping bag you want to buy. 

Final step :

         Compute :           T_c=T_0-P*R,

Where T_0, and P is what you measured and compute at step 1 2 3 and R is the R-value of the sleeping bag.

Example suppose that I sleep naked comfortably at 31 Celsius that my power output while sleeping is 39 Watt/m^2 and the sleeping bag I want to purchase has a r-value of 1.2 K m^2/watt then 

T_c=31-1.2*40=-17celsius =1.4F

If I used the EN hypothesis  i would get -11.6C (11.1) 

It's a 10F difference. Have fun.

2:31 p.m. on May 30, 2011 (EDT)
REVIEW CORPS
1,308 reviewer rep
1,072 forum posts

Brumo, you are adding some well-needed technical discussion to this forum...thank you for the information and interpretation. I've had my doubts about the EN sleeping bag test for a little while now, and you've really summed up the discrepancies nicely!

3:11 p.m. on May 30, 2011 (EDT)
171 reviewer rep
223 forum posts

Second time I see this study very interresting again. I think marmot use that technique to rate its sleeping bag.

3:15 p.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts

pillowthread said:

Brumo, you are adding some well-needed technical discussion to this forum...thank you for the information and interpretation. I've had my doubts about the EN sleeping bag test for a little while now, and you've really summed up the discrepancies nicely!

 Thanks pillowthread. 

3:23 p.m. on May 30, 2011 (EDT)
53 reviewer rep
135 forum posts

Louis-Alexis said:

Second time I see this study very interresting again. I think marmot use that technique to rate its sleeping bag.

 Where did you see it. Damn I lost my time it was already done :D.

Marmot use both US rating and EN 13537 rating. As you can see above, the EN rating is not consistant for the lithium and the never summer. They test their bag at the Thelma institute. I ask them their test for some sleeping bags and ask some questions. I never get any answer. I don't like this kind of behavior.

I have some more thought about the EN 13537 rating, but I keep that for another topic about sleeping bags designs and construction cause it is related to it.

10:57 a.m. on June 7, 2011 (EDT)
53 reviewer rep
135 forum posts
Addendum and Errata

Here is an addendum. I was finally able to  find the parameters values used in the EN test. I wasn't that far and actually for the temperature considered here, the two lines almost coincide and so the formula give the same result :

So for the average man power output we have : 36.36 watt/m^2 instead of 38

and for the T_0 we have 31.81 instead of 34.

A funny thing is that in an article of 1941 :

Gagge, A.P., Burton, A.C., Bazett, H.C. "A Practical System of Units for the Description of Heat Exchange of Man with his Environment," Science, Vol. 94, 1941, pp. 428-430.,

they observed that the average human power outpout at rest was 44.1 watt/m^2. In other words people were much warmer. This can easily be explained by the fact that houses were not heated, people were much more often outside than we are...

An easy computation shows that a sleeping bag now rated 32F would have been rated 16F in the 40's. A 0F would have been rated -20F.

You see the difference is huge (20F).

It is actually quite easy to reach this power output by acclimatizatio : Spend your time in the open air don't turn off the heat while sleeping etc... And then your body will acclimatize. Ok it may take some weeks but still.

The point here is that, as you can see, metabolism vary so much between individuals that it is pointless to try fixing  a standard temp rating. There is no standard, everyone is unique. Some people get drunk after a glass of wine while some can finish the bottle without having much negative effects. Some can run a 100 dash in 10 sec while other struggle to cross the line in less than 12 seconds. There is no standard in human physiology as far as I know.

Scientits know that. They are not stupid. So I'm asking to myself why do they decide to agree (not fully though) on a standard temp rating...

Possible answer : for money. They hope that this thing will become an obligation in europe so that any sleeping bag manufacturer will have to test their sleeping bags in their labs. At a price of more than 3000 dollars a test...

My own speculation : If i was a lab and wanted money out of the EN norm. I know I'm competing with other labs. So if I modify some parameters (the matress) the manikin,... I can have better rating than other labs. Am I paranoid. Maybe but some facts are intriguing :

http://www.outdoorindustry.org/pdf/EN13537TestLabComparisonMethod.pdf

So I'm sure manufacturers know this study and I'm sure they know which lab gives better rating.  Marmot test their bags in a Remote institute in Norway while they fill their down in the US and the KSU lab can do the job?? Actually why so much brands are testing their bags in norway while they are in the US or in germany??

Another unanswered question : If the norm was created for the consumer wellness, why does it cost from 70 to 200 USD to get a PDF copy (24pages) of the EN 13537 description?

Conclusion : I said that the EN norm is not reliable. This is a fact. But  it seems worst than that. It may just be a marketing thing to get big brands and labs happy.

11:10 a.m. on June 7, 2011 (EDT)
REVIEW CORPS
1,308 reviewer rep
1,072 forum posts

I'm pretty sure this qualifies as "blowing the doors wide open"...

You should share these conclusions with Richard Nisley over at Backpackinglight.com; as a technical researcher of the highest degree, he's likely keen to what were discussing here, but I know he'd appreciate your line of thought specific to this thread.

Once more: Bravo!

12:04 p.m. on June 7, 2011 (EDT)
87 reviewer rep
1,067 forum posts

Brumo Thanks for the second half. Just had the oppertunity to read it. I agree with pillow thread you need to share with BPl.Thats where I started to read on thermal factors. So I take it your an  engineer as well in another aspect? I am structural so factors and index computations get the best of me.LOL thanks for the information always appreciated and your insight..

1:44 p.m. on June 7, 2011 (EDT)
53 reviewer rep
135 forum posts

Thanks pillowthread.

I'm far from being an engineer, though I'm a mathematician. But I'm rather curious and I like to figure out things by myself. It's like cross word :D.

I read some stuff wrote by Richard two days ago. I was very interesting. I'll definitely put a post on BPL to share ideas. He seems to have a very good knowledge of all those stuff. 

3:23 p.m. on June 7, 2011 (EDT)
TOP 10 REVIEWER REVIEW CORPS
3,612 reviewer rep
1,248 forum posts

So don't always believe what you read on a sleeping bag label. Manufacturers pad their info to make more money? No surprises there.

I just buy a sleeping bag rated to at least 20*F lower than what I expect to experience and dress up or zip down depending on actual experiences.  I find that reading as many actual reviews from customers as possible is even more helpful.  Though everyone sleeps differently, you can get a good idea of warmth based on reviews by people who DO NOT collect advertising $$ from the companies that make the products they review. 

Hearing it from a real mathmagician (probably a statistician too) confirms my suspicions though.   

4:07 p.m. on June 7, 2011 (EDT)
53 reviewer rep
135 forum posts

The problem here is that those temp are not made buy the manufacturer but by a independent laboratory using predefined standard that were supposed to help the consumer. 

www.outdoorindustry.org/.../EN13537Mccullough062209.pdf

I like the proposition on page 8 :

Once the true variability of the standard is known (without using adjustment factors), the CEN committee could consider whether the establishment of broad temperature ranges that bags would be classified into based on their manikin test result would be a better approach to take. In other words, instead of predicting a precise temperature range for each bag based on its insulation test, they could set up five standard temperature ranges that bags could be classified into based on their insulation value. Procedures for handling “borderline cases” could be developed as well, considering the tolerance associated with the method. 

apparently those problem are known frome many years but nothing is changing. The question is why??

Notice that if a small manufacturer must test all his sleeping bags according to the EN norm : 

28*3000 dollars = 84000 dollars for western mountaineering

25*3000=75000 dollars for Rab,

37*3000=111000 for Mammut 

40*3000=120 000 dollars for marmot.

....

So two things : we'll have to pay this price. And second, high quality  small manufacturers will at best reduce their offers with few sleeping bags, at worst disappear.



4:24 p.m. on June 7, 2011 (EDT)
0 reviewer rep
1,238 forum posts

Personally I never belive much of anything written by the retail seller or the manufacture.  The only thing I give real creedence to are the specifications on the materials used.  Example, When tent manufactures give a wind speed rating on a tent that has been tested in a wind tunnel.  Wind tunnel tests are directional and the tent is set up in the best position to handle a single wind speed from one direction.  When I go into the backocuntry I'm quite often buffeted from multi directions at once with rapidly changing wind speeds and temp. conditions.  This is also not considering it may be raining, snowing, hailing, at the same time.  I will however use their wind speed specifications when backpacking in a wind tunnel.  I much prefer to wait for a while and read all the reviews I can find before pulling the trigger on an expensive item.

4:59 p.m. on June 7, 2011 (EDT)
53 reviewer rep
135 forum posts

Exactly, that's what I wrote in my post. The point is that more and more people use this rating to compare bags performance. So my goal was to convince them with facts that this standard is meaningless.

I met people on european fora that believed EN 13537 is completely standardized and that they can compare bag from brands to brands. 

6:52 p.m. on June 7, 2011 (EDT)
0 reviewer rep
245 forum posts

What I have seen here in Europe is discussions about the EN as not the standard that gives a PERFECT rating for all bags, but none has proven that any other measuring scale is better. For some people the search for the perfect overshadows the more than good enough.

Brumo do you have some alternative to EN that gives adequate readings for all persons, including sweat, food intake, heat senitivity etc?

Otto

7:31 p.m. on June 7, 2011 (EDT)
53 reviewer rep
135 forum posts

OttoStover said:

What I have seen here in Europe is discussions about the EN as not the standard that gives a PERFECT rating for all bags, but none has proven that any other measuring scale is better. For some people the search for the perfect overshadows the more than good enough.

Brumo do you have some alternative to EN that gives adequate readings for all persons, including sweat, food intake, heat senitivity etc?

Otto

 As I said, there's no way you can fix a standard, but what Dr McCullough suggest is a good idea. I would be much more honest and useful to define ranges of utilisation. 

Example :

expedition range -25 to -35,

winter  : -15 to -25,

fall : -5 to -15

etc...

These have 2 advantages. First it is more honest. Second the test could be less precise and so cost much less. Which is a good thing for small compagnies.

Actually it is funny, my brother just watched a documentary about EN norms in general :

There is 258000 pages of norms. Each municipality have to hire people just to know all those pages (which is in fact impossible). In france it cost around 2.2 billions euro per year to pay the salaries of those people. And worst, compagnies, manufacture etc... have to spend a lot of money to follow those norms. At the end it cost billions just for meaningless technocracy.

7:43 p.m. on June 7, 2011 (EDT)
53 reviewer rep
135 forum posts

Ho and the point is not so more about giving a consistent way to compare bags between brands than  give a correct temp rating. and in this respect EN fails miserably.

Example : The rab ascent endurance 900 (900gr of 650 FP) as the same temp rating so the same R value as the Valandré odin (1200 of 850 FP). So if it was a good standard you could thing that you can bring the rab ascent on the Everest of in alaska. And this is not true of course. There's no way 900gr of 650 loft as much as 1200gr of 850.

9:06 p.m. on June 7, 2011 (EDT)
130 reviewer rep
130 forum posts

Coming to the party late, but I interviewed Dr McCullough about her findings last year. I won't repeat everything I covered in my article about it, so please excuse my just posting this link. There's also some interesting discussion in the comments below the post, including comments from people using the tests here in the US and working on the standard.

http://sectionhiker.com/sleeping-bag-temperature-ratings-fact-or-fantasy/

6:53 p.m. on June 8, 2011 (EDT)
0 reviewer rep
245 forum posts

FromSagetoSnow said:

Hearing it from a real mathmagician (probably a statistician too) confirms my suspicions though.   

 I could not agree more to the term "mathmagician", and as I made some inqueries my suspicions got confirmed. First Brumo, according to my internet the Rab Ascent 900 has a comfort ENrating of -11c and the Valandre Odin has a comfort rating of -18c (some stores even claim -20c) so they aren NOT equal in rating as you claimed.

Then the passus you wrote about the EN rules and all that. What has that to do with what we are discussing here, sleeping bags and the standardised testing of those? The EN rules cover everything from birth to grave and are a set of rules for the community to behave consistently within. One may like it or dislike it, but it is another matter completely, period.

As I understood your last answer there are alternatives but noone is using them. So where does that leave me as a consumer, more or less informed? And also the simple test and category you mentioned. Is it not a even greater risk that the Valandre Odin and the Rab Ascent 900 comes into the same category then? With the EN 13537 test they are not.

Also the raving about the price for the test. Yes it seems high when you say it costs 3000$ for each bag. But when you divide it with 10000 sold units of a bag it is a mere 0,30$. OK, maybe some sell only 1000 and it is 3$ per bag, so what? I do not get annoyed over a 3$ rise in such a product, it costs me at least 100 times as much anyway.

I'm sorry Brumo I do not agree with you. I think the EN 13537 test gives me as a consumer more qualified information regarding the sleeping bags than former tests and the alternative you suggested.

Otto

8:00 p.m. on June 8, 2011 (EDT)
53 reviewer rep
135 forum posts

OttoStover said:

FromSagetoSnow said:

Hearing it from a real mathmagician (probably a statistician too) confirms my suspicions though.   

 I could not agree more to the term "mathmagician", and as I made some inqueries my suspicions got confirmed. First Brumo, according to my internet the Rab Ascent 900 has a comfort ENrating of -11c and the Valandre Odin has a comfort rating of -18c (some stores even claim -20c) so they aren NOT equal in rating as you claimed.

Then the passus you wrote about the EN rules and all that. What has that to do with what we are discussing here, sleeping bags and the standardised testing of those? The EN rules cover everything from birth to grave and are a set of rules for the community to behave consistently within. One may like it or dislike it, but it is another matter completely, period.

As I understood your last answer there are alternatives but noone is using them. So where does that leave me as a consumer, more or less informed? And also the simple test and category you mentioned. Is it not a even greater risk that the Valandre Odin and the Rab Ascent 900 comes into the same category then? With the EN 13537 test they are not.

Also the raving about the price for the test. Yes it seems high when you say it costs 3000$ for each bag. But when you divide it with 10000 sold units of a bag it is a mere 0,30$. OK, maybe some sell only 1000 and it is 3$ per bag, so what? I do not get annoyed over a 3$ rise in such a product, it costs me at least 100 times as much anyway.

I'm sorry Brumo I do not agree with you. I think the EN 13537 test gives me as a consumer more qualified information regarding the sleeping bags than former tests and the alternative you suggested.

Otto

 

Read :

http://rab.uk.com/products/sleeping-bags/ascent-endurance/ascent-endurance-900.html

 and

http://www.valandre.com/eng/Sleeping_Bags_and_Outerwear/sleeping_bags/odin.html#axzz1Oj5PWWtd

Then either click on the PDF report just next to the -42 or go at the end of the page.

With the EN 13537 temperature rating they are exactly in the same category. 

You didn't read the post and then you didn't read the correct rating. So you just disqualify yourself. 

 I must agree with you that for big manufacturers like rab it's not an issue (actually I asked them and they seems to find the price quite high as they do pretest before sending a prototype in order to save money. In the mail it was mentionned "the costly EN test."). But for small compagnies they don't sell 1000 bag a year so it's a high price for them. 

Don't be sorry. I'm not here to convince you of anything. If EN rating works fine for you it's ok.  

8:06 p.m. on June 8, 2011 (EDT)
53 reviewer rep
135 forum posts

Doubts rather than Ignorance...

October 24, 2014
Quick Reply

Please sign in to reply

 
More Topics
This forum: Older: Pack Cover Newer: USA made hiking boots?
All forums: Older: Lost Coast Information Newer: PIF gear