Doubling up sleeping bags

Matt Himmelstein wrote: THey sell thin liners that are supposed to add 15 deg or so warmth.  I have not used mine, but that's what I bought so I can extend the range of the 15 deg bag I have now.  It is small and light.
https://www.rei.com/product/797114/sea-to-summit-thermolite-reactor-extreme-sleeping-bag-liner

For car camping, I would just bring a down (or synthetic) blanket and use it over the bag.

Adding 15 degrees to the rating of a bag with just a liner is a big ask. I wouldn't go into a serious situation with a 15 degree bag and a liner like this, then expect to be as warm as a 0 degree bag. 

I have this liner, and sometimes carry it, but oftentimes the main goal is to keep the bag just that much more cleaner, as putting a stinky human that's been outside all day into a bag tends to sully it up. Washing a liner is easy. Washing a sleeping bag is less so.

A bonus no one mentioned yet of a double bag set up, if you do a synthetic outer with a down closer you'll likely maintain loft for more nights out. When you're dealing with a lot of insulation the dew point will usually land somewhere within the insulation. On nicer days you can flip the black lining out in the sun and dry out the down quick enough, but if you're hunkered down in a storm things can go bad. For a great tale about this read up on Mark Twight's thoughts on bags after the Rupal Face. 

By putting the down bag closer to your body and the synthetic outside of it you're much more likely to have the dew point land in the synthetic insulation. Any moisture/vapor in the down bag is driven out into the synthetic.
 

Not sure if it got mentioned, Western Mountaineering makes a bag that’s cut wide with the intention of being used as either a 45F summer bag or an over bag that you can slip your smaller bag into. Adds 10-15F. Its called the EverLite. 

Liam Hoefer wrote: Not sure if it got mentioned, Western Mountaineering makes a bag that’s cut wide with the intention of being used as either a 45F summer bag or an over bag that you can slip your smaller bag into. Adds 10-15F. Its called the EverLite. 

Liam, just was looking at that today!

thanks for the input. Z

Long Ranger wrote:

Adding 15 degrees to the rating of a bag with just a liner is a big ask. I wouldn't go into a serious situation with a 15 degree bag and a liner like this, then expect to be as warm as a 0 degree bag. 

I have this liner, and sometimes carry it, but oftentimes the main goal is to keep the bag just that much more cleaner, as putting a stinky human that's been outside all day into a bag tends to sully it up. Washing a liner is easy. Washing a sleeping bag is less so.

I have one of the 15 degree liners and it definitely adds warmth.  Not sure about 15 degrees worth, maybe a little more than half that, but it's so situation dependent that it's hard to accurately judge.  I've found that it works better to get your bag to be comfortable at its advertised temp rating, since most bags' temp ratings are designed more as a survivable but uncomfortable rating.  

I.e. If I use the liner in my 30 degree bag I will be cozy in it at 30 degrees, when otherwise I'd probably be chilly.

zimick wrote: Anyone here have a system for doubling bags to use in the cold?
i have an old winter bag that is finally giving up and in my older gear is a Sierra Designs bag I inherited from my sister that was made with a liner bag to give it a broad temp range and that has me thinking.
instead of springingfor a spendy full winter bag that really is limited in usability why not get a zero bag and ( thinking out loud here) a summer weight squarish bag to use over it for cold nights?
I get that the combo will be heavier, more zips, pain getting it all lined up but it seems it could work.
without a lot of looking I could get a MH Phantom Zero that is just under 3pds and add a Western Mountaineering bag that is 14oz....?
I’m ready for the insightful, the mockery and the off topic.  

Depending on where you live/ what conditions you’ll be in, I usually recommend a nice 20 degree bag. They pack small and in the summer they’re usually more than you need warmth wise. If you pair it with a good liner, it can add around 15 degrees for a lot less weight than another sleeping bag. Then in the winter, if it’s truly cold, boil water, put them in nalgenes and stick them in the bottom. (Wrapping a warm body will waste less energy) sleeping bags are usually rated for a full base layer system as well... good luck! 

One problem with doubling is that with a wrong choice of bags the outer may compress the inner by being too heavy or too tight, especially if the inner is down. It may end up being warmer than a single but not use the full insulation value of both bags.

I use a sleeping bag inside a bivy bag.  The bivy bag adds some degrees of warmth and is waterproof.  

Should we also open the debate on sleeping clothed or naked?
I've heard a debate for some time that sleeping naked is actually warmer than in clothes because the bag reflects the body heat better.  I don't have the guts to do it though in really cold weather.  I've found sleeping in my clothes (to include my puffer) keeps me toasty.
Thoughts??

That's not a debate. Dry layers in a bag large enough to accommodate them are warmer. If your layers are wet or you've got the latest sexiest 1.5lb bag fit for children and outdoor magazine editors then it's not so clear.

jdejace wrote: That's not a debate. Dry layers in a bag large enough to accommodate them are warmer. If your layers are wet or you've got the latest sexiest 1.5lb bag fit for children and outdoor magazine editors then it's not so clear.

So, are dry layers of clothes warmer, equally as warm, or less warm than dry layers of sleeping bags without clothes?

Sorry... rereading.... I think you're saying dry layers of clothes are warmer...

Dry layers + sleeping bag >> no layers + same sleeping bag.

Caveats above. If your sleeping bag is cut tight for maximum thermal efficiency/light weight then layers can be counterproductive. 

https://backpackinglight.com/forums/topic/12505/page/2/#comments

See nisley’s comment here. Down can be compressed by up to around 2.5x its fully lofted density before it loses any meaningful insulation value. Here is a graph showing what happens when you add down to a sleeping bag with a fixed baffle height:


More down (up to 2.5x) equals more warmth even if it doesn’t fully loft. The idea that sleeping bag warmth is based solely on the volume of trapped air is not correct

Paul Coakley wrote: Should we also open the debate on sleeping clothed or naked?

Problems happen if you ever need to get up from sleeping during the night for more than 10 seconds. Waking up can be a little harsh, too.

Brian Abram wrote: https://backpackinglight.com/forums/topic/12505/page/2/#comments

 Down can be compressed by up to around 2.5x its fully lofted density before it loses any meaningful insulation value.

The idea that sleeping bag warmth is based solely on the volume of trapped air is not correct

Thanks, that's interesting. If my awful maths is correct it means a fully lofted 2" of down would need to be compressed to 0.8" before losing much insulation. I think that could still happen overnight especially with a heavy artificial fill second layer or a second layer that was too tight (I'm too lazy to get out my sleeping bag and try it). In this case adding a second layer would probably still give more total insulation but not the theoretical maximum of the two combined.

I use the Sleepingo, more than satisfied with it. You can read a review here to get a better idea of what it offers: https://popular.reviews/sleeping-bags/#1_Sleepingo_Double_Sleeping_Bag