View Full Version : Sleeping bag question
I know there are a lot of variables to this, but how do manufactures come up with the degree ratings for sleeping bags. For example, wouldn't a 40 degree bag be warmer, or maybe less cooler, than the same bag using a ground pad? So would the rating be slightly higher using a ground pad?
Ground insulation is necessary in all but the warmest temperatures. Where one's body compresses the bag's loft below, the bag's insulating properties are greatly reduced. Generally, the rating assumes adequate ground insulation.
There are standards for sleeping bag ratings, but not all manufacturer's hold to them. It is highly recommended to read some reviews of the bag and try to find someone who has used it at or below the rated temperature. Also note that the rating can indicate the lowest temperature at which you can make it through the night without hypothermia setting in, not necessarily a temperature at which you would be comfortable.
johnnybgood
10-29-2013, 19:28
The degree of warmth added would be the result of insulation between you and the ground surface outside your bag not the bag itself
They make it up. Nothing scientific is done to figure out what it means to buy a 20 degree bag. We humans have too much variation in body heat generation and retention. Many hikers suggest that the rating is the temp where you freeze to death.
MuddyWaters
10-29-2013, 21:19
With high quality down, its usually based on loft height, or oz of fill.
1.5" = 40f
2" = 30F
2.5" = 20F
etc.
Many commercial mfgs will have thier products EN tested. It doesnt mean its correct for any one, but at least its relative to others.
the EN testing procedure puts a dummy inside, with temp probes attached, with a certain heating rate, on a certain rated pad, and measures temperatures. Its expensive, but more and more are doing it.
And as was said, cheap mfgs will just make it up.
This is an ollllddd post but maybe helpful for folks searching for answers about this is the future.
I read that sleeping bag ratings are based on the assumption the user has a sleeping pad with an R-value of 4
HooKooDooKu
04-16-2021, 09:40
There's more assumptions than that... such as how much warm clothing the person is wearing as well.
But those various "assumptions" are different depending upon what rating "system" or "standard" is being used.
Back when this thread was started, there was the "EN 13537" standard. But that was a European created standard, and it's details have changed over the years.
The system introduced the concept of multiple temperature ratings... "Comfort", "Lower Limit", and "Extreme" (to what temperatures will you be comfortable, uncomfortable, and minimum survival). Some manufacturers started testing with the EN 13537 standard, others started publishing Comfort/LowerLimit/Extreme rating but not using the 13537 standard. Plenty came up with their own standards, with each making different assumptions about sleeping pads and what a person was wearing, etc.
Today, the most recent standard is the ISO 23537-1:2016. But the temperature rating you see on a sleeping bag is meaningless (other than comparing the ratings for other bags by that manufacturer) unless they indicate their rating is based on this standard. And what's even better is when a sleeping bag tells you about these systems but never says they follow them (I just checked a NEMO woman's sleeping bag description at REI where they talk about the standards and how they apply to women, but they never say they used that standard).
Hookoodooku is right about the rating system.This was a topic last month on Backpacking light .
at least bags have some standards - quilt ratings are total bs, lots of people being fooled/ disappointed
swisscross
04-18-2021, 15:48
Wondering where you got those numbers...the specs on my WM megalite, 4" of loft yet rated 30 degrees.
In my experience, the rating is the temperature at which you will suffer.
I have two sleeping bags - a zPacks 10F rated full zipper bag and an Enlightened Equipment Revelation 30F quilt.
The zPacks is about 8 ounces heavier but I find that worth well worth it unless I know that temperatures will not drop into the 40s. If temperatures are in the 50s or higher, the zPacks can be too warm, as I experienced a few years ago in the front country campground of Sequoia national park prior to hiking the High Sierra Trail.
The Enlightened Equipment quilt is fine for summer backpacking and for trips in Europe where I stay in huts or, in the case of the Camino, in albergues (aka hostels).
Ultimately ratings are just a guideline. Some people are happy with the EE 30F in the high Sierra with lows near freezing. I know that I would be cold so I am fine with an extra eight ounces. I like my solution of having a 10F and 30F option.
While I have yet to try this, in theory I could use the EE revelation AND the zPacks sleeping bag in winter for more warmth if temps get into the teens or worse.
Wondering where you got those numbers...the specs on my WM megalite, 4" of loft yet rated 30 degrees.
If you’re referring to post #5 (Muddy Waters) his numbers are loft ON TOP OF YOU. Your 4” Megalite bag gap has 2” of loft on top of you equaling a 30*F bag.
His numbers are pretty much spot on, EN aside.
“gap” above is an errant autocorrect from my iPad and should not be there. :)
swisscross
04-18-2021, 22:26
“gap” above is an errant autocorrect from my iPad and should not be there. :)
Not an answer...where did the numbers come from?
Have taken my bag to 12 with no issues. Just reinforcing manufactures numbers mean little.
Not an answer...where did the numbers come from?
Are you always so abrasive?
Those “numbers”, as anyone can tell you that has been at this for a bit, go back to at least the 1960’s. With down bags loft has always been the way to generally measure a bags effectiveness. Those of us that came of age around that era pretty well have those numbers committed to memory, and undoubtedly that’s where Muddy Waters got them. They were essentially true then, and remain so now all things being equal.