Is there practical efficacy to nesting sleeping bags?

Do a search of the forums here. This was discussed not too long ago. You should be able to turn up good info.

It is not as thermally efficient as using one bag which is adequate to the coldest temps. that you will encounter. However, I have often done it and in some pretty harsh situations, due to being a "starving student", long ago.

I used to put my old Chouinard Thermolite synthetic bag INSIDE the Feathered Friends GT-down "Overbag" which I just gave a friend for his little daughter and it worked very well. But, a dedicated winter bag is lighter for the warmth and much easier to compress and pack.

Some will prefer the down INSIDE of the synthetic, but, I have always felt that this would allow more moisture to be trapped in the down and have found the way I did it worked best, YMMV.

If the two 35s will zip together, do that, and then throw the opened out 20 over the top as a quilt. You'll need to shove a jacket in between your shoulders to stop drafts

IIRC, if you spoon you don't need a draft stopper and the sleep system would net you 10-15 degrees less than if solo so your 35 degree bags would be good to 25 or maybe even 20. YMMV of course.

Another approach that fits the starvin' student profile: Take along your heaviest bag and a Heatsheets emergency bivy, which weighs in at 3.5 oz, including the storage bag, and costs about 10 bucks. The Heetsheets is more stretchy than the usual mylar e-bivy, so you can get multiple uses out of it.

Get into the Heatsheets first, and then into your bag. I've found I can get at least 15 degrees out of the Heatsheets at minimal cost, both in terms of $$ and weight (and volume, too — the Heatsheets folds up to practically nuthin'). It surely beats spending $350 on a true winter bag.

But then again, the winters aren't that severe in Ohio.

Stargazer

Wamlite three in-one-bags layers down tops together to creat their warmest winter bags. The layers zip in.

http://www.warmlite.com/bags_In.htm

Zipping additional top layers onto a bag, as Stephenson's do is not quite the same as nesting different bags and is STILL less thermally efficient than using an adequate bag.

I once bought a highly touted Swedish "expedition" bag, double shelled and zip-together and, at below 0*F, although I was told it would do -40, no problem, I bloodywell froze my butt.

I sold it and bought one of the early, all hotcut, GT-down bags from Marmot Mtn. Works when Eric Reynolds managed it. THIS single bag, weighing slightly LESS than the double Swedish pos, WOULD keep me toasty to -20*F and I did Ok in it, inside my firt Early Winters GT bivy and in a tent at -30 to -40 and, THAT is VERY cold, believe me!

The SHELL material is CONDUCTOR and thus the more of it you have equals more heat LOSS and that is what you do not want. Soooo, I would not buy a double bag or a Warmlite, which I never have cared for.

Try an ID Primaliner inside a medium down bag, this has worked well for me.

I've nested down bags for years in winter. My setup uses a rectangular bag over my mummy bag. I've no experience combining down/synthetic however.
The solution is heavier than a single bag of equal temp rating, but more economical for me.

PHDesign makes an outer bag specifically designed to combine over their lightweight bags, with a looser cut. You need the inner dimensions of the outer bag to be about the same as the lofted outer dimensions of the inner bag, otherwise you're squashing the inner bag and preventing it from lofting properly.

I haven't experimented myself, but I've also seen recommendations for synthetic on the outside if you're mixing. Both for better resistance to moisture coming from outside, and because (you hope!) the dew point for your internally generated moisture on the way out is nearer to the outer surface than the inner, and you'd prefer to have any condensation occurring in the synthetic rather than in the down.

More info on this topic here:

http://www.andy-kirkpatrick.com/site/main_articles/double_up/

Thank you all for your insights. I've got some initial ideas to try out. How much temperature benefit do you think I might could get out of nesting a down bag inside a 45* synthetic bag? 10*, 15*, 20*???

The 45* bags I've got are the Mountain Hardwear Lamina 45 bags (Micro Thermo insulation, which is pretty well reviewed). Actual bag weight is 25.4oz, and they compress amazingly small (~6" sphere).

The 35* bags are Exped Wallcreeper bags (I think they've recently re-rated them to 30* without making any changes to design; marketing thing, I think). Those bags weigh 31.7oz, and also compress pretty small, maybe 6"x11"?

Total, the 45* synth and the 30-35* down would be a weight of 57.1 oz, which I know is heavy, but it compresses smaller and is 6.4oz lighter than the 0* synth bags we have… especially if only one of us needs to double-bag and the other takes the GoLite Feather 20… or if we double-bag the GoLite Feather 20 with the other MH 45* bag for my GF since she sleeps colder than I do.

I'm trying to do a weight/space comparison for backcountry use with the gear I've already got. Obviously, the best long-term solution is to look for a great deal on a second 800+ down bag, but that's not worth the $ right now. So I'm looking for the next best solution.

My guess is that it is going to be a several year process to truly go ultralight. Getting under 20# base has been pretty easy; getting down to 15# seems pretty doable in the near future. Hitting that magic 12# seems doable for summer, but I don't see it for winter anytime soon… But I appreciate all of your help in getting there.

on the inside of the bag! toasty! i actually first tried it over a down bag in a cold damp hut. the result was not good. i think i must have had some mild hypothermia!

fantastic piece. cheap. bright orange — would be awesome to wave at a helicopter.

I agree — probably 15F out of it!

used to have a fantastic fairydown down liner bag. didn't pick a package up at a post office in time and it was "returned to sender" — the sender being me a half world away at the time of shipment. never tracked down that box of goodies. don't know if they still make them. they were bought out by macpac. it doubled as about a 50F bag.

No 2 nested full bags are going to be UL.

Just guessing I would say adding a 45dF bag would add about 15dF to the temp rating.

Also if I were to take an approach to something like this I would probably use a tight bag inside a Montbell SS, or something like that.

More of an UL option might be to use a Climasheild over quilt instead of two bags. An UL 45dF quilt should weigh about 14 oz.

A better UL option would be nested quilts. like a BPL 90 inside a Golite ultra 20.

That would weigh about 32 oz and good to maybe 10dF.

Not 100% on if that would be a good match. I am building a custom sized summer quilt to use inside my ultra 20 made to fit.

Where can you buy heatsheets?

I'm thinking about getting a down half-bag to use with a down jacket under my golite ultra 20.

I've seen one I liked online, but I can't remember where! Anybody have any ideas? It was a well known bag maker, just can't think of it…

Surely a Heatsheets bivvy will act like a VBL? Not a good idea over a down bag.

>Surely a Heatsheets bivvy will act like a VBL? Not a good idea over a down bag.

Exactly right. You have to use it inside the bag,

Stargazer

P.S. Can't remember where I got mine, but I'm sure they're available from the usual sources: REI, Campmor, etc.

Vapor barrier over down bag? I was making light of my own silly mistake! i use it between patagonia cap 4 top and bottoms and my bag. Don't know how it would go against skin. Hmmm. I have the heavier duty orange one. it doesn't make much noise and it lasts a long time.

heatsheets made by Adventure Medical. Just google — adventure medical heatsheet There are a few options.

Here's a quick article about the two models Adventure Medical makes:

http://gearjunkie.com/adventure-medical-kits-thermo-lite-2-bivvy-heatsheets-bivvy

This site has both models on sale for ~30% off, and free shipping with a $35 order. Haven't used this site before, so YMMV:

http://www.high-mountain-outfitters.com/Survival-Packs_c25.htm