Sleeping Bag Ratings Explained

Sleeping bags typically have a temperature rating.  If you're looking to actually get some sleep while backpacking, you'd darned well better pay attention to the rating.  

Spring snow in the mountains.  Gonna get chilly tonight.  Is your sleeping bag up to the task?

Can I rely on the temperature rating? 

In other words, if it's 32F/0C at night will I be comfortable in a sleeping bag that's rated 32F/0C?  Simple answer:  No.  Or at least, most probably not.  

When a manufacturer, at least in the United States, lists a temperature rating, there is no universally accepted standard.  There are no regulations in the US that govern what a manufacturer lists on its sleeping bag.

What!?  No standard!?  So, could the Sales Department be making these ratings?

Yep, they sure could, and with some companies it looks like that's exactly what is happening.  But let's look into the details.

EN and ISO ratings

There is however an exception to my "there are no standards" statement:  EN or ISO ratings.  There is some variance based on who does the testing, but at least EN or ISO sleeping bag ratings have some basis in fact.  Here are the four ratings that come from EN/ISO tests.  These are my words to describe them.  Different manufacturers use different wording; you may have to do some homework here.

• Upper Limit - If you use this sleeping bag in temperatures above this number, you'll be too hot.  Most manufacturers don't even list this limit.
• Comfort Limit - The majority of people will sleep comfortably in this sleeping bag at or above this temperature.  Note that sometimes this is called the "Women's limit" which I think is a poor description.
• Lower Limit - Most people will feel cold if they sleep in a bag at this temperature, but at least you'll get some sleep.  Young, fit males may actually sleep well in this bag at this temperature (Men tend to sleep warmer than women).  Note that sometimes this is called the "Men's limit" which, again, I think is a poor description.
• Extreme Limit - This is the "maybe you won't die" limit.  This limit is mainly for mountaineers who might pack a sleeping bag just for an emergency.  This limit is not for sleeping.  This is just about trying not to be dead.  You absolutely could get frostbite, and you might lose some fingers and toes – permanently.  Many manufacturers don't list this limit.

Most manufacturers just list the Comfort and Lower limits.  The rating contained in the name of the bag is usually the lower limit.  For example, per their website, the Mountain Hardwear Bishop Pass 30 sleeping bag is rated as follows:

• EN Comfort Limit:  40 F/4 C
• EN Lower Limit :  30 F/-1 C

Notice that the rating embedded in the name of the sleeping bag is the lower limit.  Most people will feel cold at the stated rating of the bag (30 F/-1 C) but will (hopefully) get at least some sleep.  If you want to sleep well, the Comfort rating is the one to pay attention to.  If you select a bag based on the Comfort rating, you've got a little margin for error if the temperature drops unexpectedly.  If you select a bag based on the Lower Limit, then you've got no margin for error.  

22 Fahrenheit/-5 Celsius. 
I brought a 40 F/4 C Comfort rated bag. It was miserable.

Once, in mid-May, I was out in the San Gorgonio wilderness at about 8,000' elevation.  The predicted low was 38 F/3 C.  I ignored my own rules and tried to save weight and brought only a 40 F/4 C Comfort rated bag.  Hey, it's spring, right?  How cold could it possibly get?  The actual low according to my thermometer was 22 F/-5 C.  I was OK in the sense I was not in danger of frostbite or hypothermia, but it sure was miserable.  I hardly slept at all.  Lesson learned.  Don't do what I did.

What if there is no EN or ISO rating?

Well, then you have to go on the reputation of the company.  You have to take their word for it.  Most companies sell bags based on the Lower Limit.  To get some idea of  the Comfort Limit, add ten to whatever rating is in the title of the bag.  For example, if the bag is advertised as the "BigFoot 40," assume a comfort rating of about 50 F/10 C, if you trust the company.

Beware of some companies.  In my experience, any bag coming from Coleman is to be looked at with extreme skepticism.  I once used a borrowed Coleman bag that said 32 F/0 C on the box.  Ha!  I wouldn't take that bag into anything below 50 F/10 C.  Their rating was all but outright fraud.

Likewise, Teton Sports' ratings are suspect.  I've seen them advertise their bags using the Extreme rating.  The Extreme rating is often 30 F degrees below the Lower Limit (about 40 F degrees below the Comfort Limit).  Using the Extreme rating as a bag's advertised rating is deceptive and dangerous.  Shame on Teton Sports.

For all sleeping bags EN/ISO rated or not

For all sleeping bags, regardless of whether or not they have an EN or ISO rating, do your research.  Read reviews.  Ask around.  Look at customer feedback on sites that sell the sleeping bag.  Gear reviews and rankings on sites like outdoorgearlab.com, The Trek, Halfway Anywhere, and Adventure Alan are worth looking into.  Research twice; buy once.  Having to buy another bag because you went cheap on the first one doesn't save money.  I speak from experience.

I hope this is helpful.  Please leave any feed back you may have in the comments.

Good luck out there, and... sleep well.

Thanks for joining me,

HJ