Doubling up sleeping bags

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.  

Valandre makes high-volume, super high quality down sleeping bags meant to be slept in w/a down suit or down parka.  I used an old 15F Marmot down bag inside of a Valandre 20F bag like this on Denali for 5weeks and it was solid.  Add a silk liner and a BD Winter bivy sac for more warmth

I don't know if it's ideal, but I can attest that I think it works.

I'm currently on a long bike trip, and the temps got way to cold for my old summer bag. But I didn't have a ton of money, so I bought a new 30-degree down bag cause it was on the cheaper end. I've been using my old synthetic inside my new down bag, and I've been keeping really toasty in the 20s and high tens. I have a cheap liner too, i use it more to keep the bag clean though and I don't think it adds much insulation. The only downside is i now bike with 2 bags, but to me it was better than spending a few hundred on a lower-rated one, at least for now.

*it's a tad annoying to zip them both, because i have to zip the inner like 1/2 the way, then the outer 1/3 the way, then the innder to 2/3, ect...

Yes. For expeditions in the Alaska range I like to take a 0 degree down bag and a +30 degree hydrophobic down or light synthetic bag. I'v used this system in the Himalaya as well. Its great to have a couple of sleeping bag options and also be able to double them up for cold nights in camp. The light bag goes along for 1 or 2 bivy missions or as emergency gear on summit pushes. Its nice for keeping boot liners and electronics warm as well - they can go in-between the two bags which is more comfortable for sleeping. 

It works fine and is pretty common among backpackers, just need to size correctly so that you don't compress the insulation in either of them. Or buy one with a full length zip, open it all the way up and lay it on top. Or buy a proper quilt.

Here are some temp charts to give you a basic idea.

https://support.enlightenedequipment.com/hc/en-us/articles/115002770588-How-to-layer-quilts-for-sub-zero-camping

https://nunatakusa.com/apex-quilts/102-gamut-climashield-apex-quilt.html

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.  

Done it for below zero snow camping, I used my ok 30deg bag and a cheap walmart bag. Twas toasty.

It definitely works.

I wouldn’t doit for backpacking, for reasons you have stated,  but it works very well for car camping. I have a 20 degree mummy bag that is very old, and i also have a cheap square sleeping bag from Walmart that doesn’t even have a rating that I’m aware of. But it might be 40 degrees? (From the kids’ sleepover days, LOL)

The combination of putting the mummy bag inside the square bag has kept me toasty and comfy in sub-20 degree weather,  many times. 

I do this at home. I can't be the only one.

I have a wal mart bag for car camping so I keep my nice one clean, but on winter trips I stuff my nice one in side the wal mart one and it keeps me super toasty. 

Long Ranger wrote: I do this at home. I can't be the only one.

Guilty!

i had a double bag system that I used for several years. It works but is heavy which depending on the need may not be ideal. At this point I have 4 different sleeping bags, warm, cold, damn cold, real cold.

I put a shitty walmart 20 degree bag in a north face 0 degree bag and brought it down to -25F no issues. I have since bought a nicer 20 degree bag. Works, but takes up space. 3 piece military sleeping bags do the same thing, so its not uncommon.

Long Ranger wrote: I do this at home. I can't be the only one.

Well yeah, can’t keep it stuffed and hanging it in my closet takes too much space so sleeping bag comforter is the only practical solution 

kevin deweese wrote:

Well yeah, can’t keep it stuffed and hanging it in my closet takes too much space so sleeping bag comforter is the only practical solution 

And proof that the Onion is America's finest news source.

I have a Valandre Mirage sleeping bag for sale, which works as a great outer bag, and is ultra-light.
Size Medium, 32F, 26.3oz

And a Valandre Lafayette sleeping bag for sale, which is designed specifically for high-altitude technical alpinists going light and fast and sleeping in it in their down suit.
Size Large, 23F, 39oz

I did this for winter backpacking with my kids, when my daughter was too little to carry all of her own stuff; I would pack a summer bag in her pack, and another one in mine, and put one inside the other for her to sleep in. She called it The Floof and she was toasty warm.

jdejace wrote: It works fine and is pretty common among backpackers, just need to size correctly so that you don't compress the insulation in either of them. Or buy one with a full length zip, open it all the way up and lay it on top. Or buy a proper quilt.

Here are some temp charts to give you a basic idea.

https://support.enlightenedequipment.com/hc/en-us/articles/115002770588-How-to-layer-quilts-for-sub-zero-camping

https://nunatakusa.com/apex-quilts/102-gamut-climashield-apex-quilt.html

Jdejace - awesome links, thank you

Like you said doubling bags is a pain.  However a down or synthetic quilt strapped over the top of you're sleeping bag isn't at all uncomfortable.  If you are doing an extended winter trip you could try a synthetic quilt which would do better with the moisture that inevitably collects on the outer layer. 

I have a couple dry down quilts that I've been impressed with.  Lots of variations available, including ones with foot pockets to better stay in place.  Use them alone or as an add-on to your bag.

I can say that this definitely works. I tend to hammock camp year round and when the temp is said to be around 20F or less, I use my 20F Kelty Dridown bag and a 40F Ozark Trail bag from Walmart. Never been cold when using both.

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.