REI blog-I think they’re wrong.

I agree

Total insulation is the sum of the individual insulations.

Although, for example, if there isn’t enough room inside for your clothes insulation to fully loft, it will be less.  Or if you got wet from sweat.  Other exceptions like those.

I wear a down vest inside my sleeping bag.  I roll around so I keep sleeping on top of one side’s insulation.  It loses some loft and gets lumpy when I roll onto other side.

They may be missing a few claifiers here.  If your clothes were damp, then their statement may be true to some extent.  Removing those clothes will reduce the amount of water in the sleeping system and you would probably warm up faster.  Spitballing here.

I don’t know the overall context of the blog’s claim, so it’s hard to say definitively, but it sounds like they’re talking about situations where adding clothing as insulation inside the bag results in more condensation happening inside the bag’s insulation.  Perhaps that’s what they mean by the bag not warming up properly?

Poorly worded at best.

I generally get in my bag with socks, base layer top and bottom, BUFF, and a hat, then add clothing if I wake up cold.

<p style=”text-align: left;”>They are wrong. The only exception is if your clothes are so bulky they are compressing the loft if the insulation. Other than that, dumb.</p>

The blogger seems to assume that it is the sleeping bag that makes you warm not the metabolism of the human body.

There were echoes of this assumption in the first edition of Colin Fletcher’s book The Complete Walker where he recommended that you sleep in your down bag nearly naked.

The entire post is a little different:

“First, a quick lesson on how sleeping bags work: They trap your body heat within the down (or downlike synthetic) insulation. But a sleeping bag cannot do its job if (1) you’re not emitting heat inside the sack or (2) the insulation is compressed. Regardless of its stated temp rating, a sleeping bag is only as warm as the sleeping strategy zipped inside it.

When you wear extra clothes to bed when camping, you create more barriers between your body heat and the insulation of your sleeping bag. If those layers aren’t very permeable (like a waterproof jacket or puffer coat), then your sleeping bag won’t warm up properly and you’ll ultimately be relying on the insulating properties of your clothes instead.

If you wear so many layers that you compress your sleeping bag, preventing the down or synthetic fill from lofting, it loses its insulation power, anyway.

It’s counterintuitive, but the best thing to wear inside a sleeping bag is often a set of breathable, moisture-wicking base layers. Yes, peeling off your expedition puffy before you go to bed might be the most miserable moment on your camping trip, but after a few minutes of shivering, you might be surprised how quickly the heat turns on.”

And one of the comments below the post:

“The tip about more layers in a sleeping bag can’t be right. Insulation, whether it’s clothes or sleeping bag, keeps you warm by reducing the rate of heat transfer from your body to the environment. More insulation will keep you warmer, just like wearing a thicker base layer under a down jacket will keep you warmer.

You’re right about not wanting to compress a down sleeping bag, as that reduces the effectiveness of the insulation, but you’d have to wear a lot of layers to compress the down that’s resting on top of your body.”

+1 on Bruce Tolley’s comment. I recall when sleeping nearly naked seemed strange, but was standard operating procedure for me and the backpackers I knew.

By 1974 Colin Fletcher in The New Complete Walker advised wearing many clothes inside your sleeping bag to start, because it was easier to remove them if too hot, than to put them on if too cold. Subject to personal experience.

He even recommended sleeping with the bag open and draped over you like a blanket on warmer nights, with your feet tucked into the footbox. Much like what we call a quilt almost 50 years later.

— Rex

It’s an old myth going back decades of not wearing clothes in sleeping bags. It won’t die. REI should be called out.

So, if clothes-under-down doesn’t work…how does a puffy coat work at all?  Or better, how does a belay jacket work?  Or what about a hypo wrap?  All of those have layers – sometimes many – between the body and the down.  Serious question. 🤔

I happened to sleep in thermals this weekend, and it seemed to help my bag loft a little better in the damp weather, presumably drying it out faster. So it might be a little more complicated.

Also, the sum of the insulation isn’t the only factor, the thermal conductivity of the materials affects the performance too.

Some people at REI know what they are doing; some don’t.

I can’t tell you how many times I have been told by an REI boot sales person that Gortex boots are more breathable than the same model non-Gortex boots!!!!

Not just REI though, a lot of gear debates are anecdotal when it comes hard sciencey things. At least with sleeping bag ratings there was enough money involved it made sense to nail things down with professional scientists and standards comities to put the arguments to rest. :)

I’ve overheard this same trope by an REI salesman in the store…admittedly to an attractive young woman.  Sigh.

On the other hand, IF you are hypothermic, you will need the body heat of someone else to help heat your bag, and both of you should wear little clothing.  Perhaps that’s where this trope gets it’s origins…

On the other hand, IF you are hypothermic, you will need the body heat of someone else to help heat your bag, and both of you should wear little clothing. Perhaps that’s where this trope gets it’s origins…

Not necessarily in either case, but supplementary heat can help in certain situations; in others, it’s not necessary…and sometimes not advisable.  If you do need supplementary heat – i.e. shivering has lowered to the point of being ineffective – and can spend the time to do so, hot water bottles at the important locations can make a big difference.  Body heat also works as long as you’re not endangering yourself in the process.  Personally, I like hypo wraps: go full burrito and let them bake for awhile.

On the other hand, IF you are hypothermic, you will need the body heat of someone else to help heat your bag, and both of you should wear little clothing.

I believe that concept revolves around the idea your hypothermic due to most or all of your clothing being wet, in a cold environment. So getting out of them to warm up. Whereas, if you have dry clothing to change into, as well as a warm sleeping bag, and extra person, that could apply. I think in most scenarios in the backcountry very little to no one will have an extra change of clothes. Perhaps just dry base layers. So getting down to barely nothing makes sense there. And then a buddy of course. I backpack solo most the time, so I’m screwed

NOLS currently teaches that wet clothing (within reason etc) is actually fine in the burrito method, as long as it’s not touching the skin since the core issue is thermal conductivity.

I backpack solo most the time, so I’m screwed

Nah.  Hot water bottles are your friend in that scenario, as is early recognition of symptoms.  If one gets too cold: pull over and layer up, tramp around and exercise until you warm up, or get some hot nourishment in your system and get in the sleeping bag.  If all else fails, punch the rescue button.

NOLS currently teaches that wet clothing (within reason etc) is actually fine in the burrito method, as long as it’s not touching the skin since the core issue is thermal conductivity.

Correctamundo…and if you can’t get all the wet clothing off, do the best you can and make a toasty snack wrap anyway.  Also, “core” issue made me laugh.

Hey, at least they got us discussing the REI blog. I never even knew there was such a thing.

https://www.sitkagear.com/experience/a-navy-seal-rewarming-drill

Good article. 👍

John used to command the Navy SEAL training base here in Kodiak where I live; he used his trainees to figure out the best ways to deal with hypothermia.   https://www.sitkagear.com/experience/a-navy-seal-rewarming-drill