Temperature Rating of Sea to Summit Spark SpIII Down:

EN13537: 2012 Comfort: -2°C / 29°F
EN13537: 2012 Comfort Limit: -8°C / 18°F
EN13537: 2012 Extreme: -26°C / -15°F

Comfort — the temperature at which a standard female can expect to sleep comfortably in a relaxed position.

Lower Limit(Comfort) — the temperature at which a standard male can sleep for eight hours in a curled position without waking.

Extreme — the minimum temperature at which a standard female can remain for six hours without risk of death from hypothermia (though frostbite is still possible)
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Think how you feel coldness is as personal and individual as your preferred sleeping position.
To sleep comfortable and warm my first attention goes the mats. Sleeping bag and mats have to function together to provide warm and relaxed sleep if you suffer sometimes from back problems like me. Last item I use in coldness is a merino wool cap.

I ignore the extreme rating. I would only look at this if I will go mountain climbing in high altitudes or too regions known for strong wind. For me just a value of safetyness for extreme conditions.

I want to sleep relaxed and I use the layer principle to avoid starting sweating. Sweating means getting awake and opening the sleeping bag to regulate your personal climate feeling. So not a relaxed sleep if you have to do this a couple of times in the night.

Normally I sleep in T-shirt and short underwear.
If it`s getting cold I use long merino underwear. If it`s getting more cold I add a pure silk inliner to this which adds 5°C to 8°C. This liner I use if it is too warm for the sleeping bag.
Will the temperature fall more down and I got awake through freezing I cover my sleeping bag with a rescue blanket(Polyester/Aluminium Foil).
If I know I could get cold I always carry 3 packs of rescue blankets with me because they small, lightweigt and you can use them as a reflection layer between mats and your sleeping bag too.

I tried out some sleeping bags/mats and I got a lot of product advices. Finally I think everybody has to find out yourself what works best. I change my gear as my needs change, this mostly more by age than by adventure driven.

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What's this swapping between men and women for temperature ratings? If there's a real difference (= ratings from experimental evidence) between men and women's experience in the same bag they should provide 'his n hers' ratings. If women do sleep warmer / colder in general it's not much help to me. Having said that, none of the rating on bags are that much help. I much to prefer to 'feel the cloth' as they say and make my own assessment.

How cold you can get in a bag without suffering some sort of consequence does seem to what the marketing people zero in on. It's as if the cold rating is some kind of macho statement where the better you buy the more it reflects on your status - "minus 20C, ha, you didn't buy one of those did you. They must have seen you coming. You'll freeze to death at festivals in that. Look at this one, this is what you should've got but I suppose budget was the problem. Rated -25C and stuffed full of the best quality goose down. Feel that quality; go on, feel it, rub it between your fingers, pat that padding, see how thick it is. That's what proper insulation feels like, not like those wafer thin cheap feathers shoved into your bag. Chicken's probably still running round somewhere looking for them".

What's never mentioned and rarely taken into account is how they cope in warm weather. Dump full length zips, build in a box foot and a mummy style head surround and you can get a few more degrees of cold rating for your marketing but it makes the bag almost unusable in warm weather. I'd much rather have a long zip so the bag can be opened out and used like a throwover when it's warm. The zip might make for a cold spot at the bag's limits but I'll trade that happily for some warm weather versatility. For the last couple of long bike trips we've dumped sleeping bags altogether and used domestic down filled duvets. A couple of them came secondhand from places like Craigslist and cost next to nothing.

This has mainly to do with the lower metabolic rate and lower muscle ratio of women.

The body heats itself through biochemical activities called metabolism.
Non active muscles add ca. 20% to body temperature. If you are getting active with muscles work e.g. sport than muscles work produces heat up to 2KW. That`s the reason why you start sweating when you do a hard workout.

Around 15% of body heat is produced by the brain. Why the brain is hidden in the bone box called skull and isolation tissue like fat oder muscle tissue is missing you will start automatically wearing a cap when you feel loosing heat.

If the body temperature gets too warm, heat must be evaporated to secure the metabolism function. 90% of produced body heat will evaporate over the skin because it is the organ with the biggest surface(~2sqm). 10% of heat will be evaporated through breathing. Women who have generally a lower metabolism rate evaporate less heat over the skin which is the reason why they faster get cold compared to men. If they evaporate less heat over the skin, they need a warmer sleeping bag.

Women normally also have a lower muscles ratio than men. In relation to body weight women have a muscles mass of 25 -35%. Men do have 40 - 50%.

When you sleep your muscles aren`t active but the metabolism is still supplying energy in form of oxygen, glucose, fat and protein to them to keep them ready and in shape for suddenly actions (leftover from our evolution and the reason why we loose body weight if we are undersaturated with calories and why we gain fat/muscles if we are oversaturated with calories during sleeping ).

The difference of the muscle/body weight ratio and the lower metabolism is the reason why women feel faster cold. Think every men knows this in form of discussions to heat up the room or by cold feet in bed...

And it`s the reason why women`s temperature feeling is taken to norm sleeping bags.

Fair deal I think.

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Yes, I'm pretty familiar with metabolism. A biochemistry degree + seven years in a research lab gave me a reasonable grounding in the theory, and running (another) ultramarathon last weekend made me very aware of how it works in practice.

My comment about men and women was more one about how the brochure / web site (or wherever the quote came from) seemingly cherry picks the information that shows their product in its best light. I wouldn't be surprised if the next version shoves a pig inside the bag and uses whatever temperature it feels comfortable at in their advertising: "a great night's sleep at -40C say our test porkers; and it protects down to liquid nitrogen temperatures so it should easily be good enough for any nuclear winter our politicians generate while trying to fix global warming. Buy now - 20% off stock clearance offer."

Couldn`t know that you are professional but thought maybe someone didn`t know....
My RESPECT for ultramarathoning

As an online vendor you have to decide which kind of details you offer to convert interest into an easy sale.

Being in sales all my life means being in direct contact with critical thinking buyers and at once delivering satisfying answers to every kind of stupid and intelligent questions. By this I can tell you that intellignet questions got less and less over the years.

Meanwhile a lot of buyers are only interested in customer reviews and often these are the effective arguments to drive a sale. These type of buyers is steadly growing, they ask more on facebook or on amazon than in forum or to the manufacturer/distrbutor.

Sorry but as ignorant the buyer group grows as easy it is to sell bullshit with nice buzz words and funky graphics. Makes me earning money much easier...So with your words pigs could have a potential in future to be a real sales argument...

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The phrase 'pig in a poke' is what I had in mind.

I guess 'honest, decent and truthful' is laughably simplistic in todays sales environment. One step ahead of the police is probably closer to it.

I've been buying and using cold-weather sleeping bags since the seventies--before that, too, if you include those gigantic, kapok-filled monstrosities so common before the advent of modern synthetics. That being the case, I can report that you couldn't really trust temperature ratings back then, either. Many companies rated their bags for survival (i.e., you probably won't die during the night at this temperature) but described their ratings as if for comfort.

More reliable ratings could be guessed-at based on measurements of actual loft--same as today, although the manufacturers were apparently very good at fluffing and plumping to achieve maximum measurable loft without much bearing on what happened during actual usage. I note that the link given by the OP doesn't seem to offer loft measurements, and this alone would rule out a sight-unseen purchase in my book. 50 years ago, as today, the buyer had to draw their own conclusions based on whatever scanty data was provided--and tune out the sales staff unless by chance in the presence of one who was both experienced and honest.

I've always discounted temperature ratings by at least 20 degrees F, often more. I've discounted further to allow for damp insulation when appropriate, and further still if not planning to use a tent--a small tent is worth 10 or 15 degrees, a larger tent somewhat less. Then I try to allow for general states of exhaustion or inadequate blood sugar, either of which makes me sleep much colder. My resistance to cold (or ability to generate warmth) has deteriorated as I've gotten older, too. In all respects, YMMV.

Mark

Reminds me of an aircraft mechanic I once met, he was changing a bearing which had been dunked in liquid nitrogen to shrink it. The company provided heavily insulated gloves to handle it, but he evidently thought they would be OK to use to pick the bearing up out of the liquid. Of course the liquid soaked straight into the glove....

Thanks for the discussion, so it's exactly what I thought, just a number to rate one against another and doesn't actually tell me anything useful unless I have extensive experience of at least one sleeping bag already rated against that standard.

So for my first bag I need to just buy one and see how it goes, based on the advice of a shop assistant and some YouTube reviews

May as well ask "what's the best tent/oil/helmet/travel bike"

There are plenty of review sites around though - do a few searches for "best 3 seasons sleeping bag" or whatever. By the time you've read through a bunch of those you should have a fair idea of what brands and models fit your bill. In my case I was surprised to find fit came into it as well - the first one I got was way too tight round the shoulders, so being able to try them on in the shop is a plus.

Honestly, for camping gear this is a reasonable approach. Combine "buy a cheap sleeping bag and see how it goes" with "take a short trip and see how it goes". A basic piece of camping gear from a discount sports store will either a) let you understand what you hate about it in detail, so that you can then decide for yourself how much money it's worth to you to not experience those downsides and shop accordingly, or b) actually work just fine for the limited purposes you have for it.

Hello

Yes, you have to buy your first bag and figure out what you need.
But, just don't buy anything, go to a store that is specialized on quality bags and has sales personal with knowlegde above reading what's on the price tag.

Youtube can be a good help if you find the right channels, stay away from influencers and "survival-guys".

sushi

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My RTW:
http://www.youtube.com/user/MrXt660ztenere