A two bag winter sleeping system

by backpackingbongos

When planning my trip to the Highlands at the Easter weekend I knew that it would be cold.  My current sleeping bag which I pretty much use all year except for the warmest months is a PHD Hispar 500.  Although a great bag and very light I personally find that I am cold using it in temperatures much below freezing.  It is meant to be rated to -15C, however I think that my frozen corpse would have to be retrieved from my tent if I used it in those conditions.  For my personal comfort I think that I need a 800 gramme fill bag for winter temperatures.  Also I find that after each night in winter conditions my sleeping bag gets less and less efficient.  This is because all that lovely warm air that I create in the night condenses on the outside of the bag.  Have you wondered why the end of your sleeping bag is damp, even though it has not come into contact with your tent?  If you don’t have a chance to air it, all that moisture builds up reducing the efficiency of the expensive down.

With the threat of temperatures falling below -10C I had to think about how I would keep myself warm.  Also I would be out for four nights, possibly without the chance of airing my bag.  Andy Kirkpatrick has written a great piece called ‘Double up‘ in which he discussed the benefits of using a down inner with a synthetic outer.  The general idea is for your body moisture to condense on the outside of the synthetic bag, leaving the inner down bag dry and fluffy.  I though that I would give it a go for this trip.  My summer bag is a Mountain Equipment Helium 400, weighing in at 780 grammes.  Digging around my kit cupboard I discovered my ancient synthetic Mountain Equipment Skywalker U/L, weighing in at 740 grammes.  Okay, I’m sure that 1520 grammes is enough to make many of you out there weep.   However I was happy enough to carry that weight as a bit of an experiment.

One thing that is essential is that the outer bag is wider than the inner bag.  If this is not the case the down will not have the chance to loft, rendering the whole system useless.  Happily synthetic bags are often cut more generously than down ones and this was the case with my bags.

The extra bulk was noticeable when packing but I easily managed to get them with my bulky down mat and five days food into my ULA Catalyst pack.  In camp it was good to be able to have a synthetic bag that I could crawl into fully clothed without worrying about my dirty clothing.  This was great for general camp duties such as cooking and eating as I did not have to worry about soiling the bag.  I carry a set of ‘bed clothes’ to change into when finally turning in for the night (nicely warmed inside my down jacket before putting on!).

I have to say that the two bag system worked really well in what was probably my coldest nights out wild camping.  The first night as I was pitching, my tent was covered in frost before I had even finished.  Even at 7.00pm is was already -4C.  I have no idea how far the temperature plunged during the night because I had a great warm nights sleep.  Admittedly it was a bit of a faff getting into both bags, especially as the Helium is narrow and restrictive.  For the first three nights I slept in until past 9.00am so the tent was like a sauna with everything dry when I got up.  However on the final morning I was up at 6.45am and woke to find that the outer bag was frozen solid.  The foot and chest areas were crunchy with ice.


To add insult to injury when I sat up I received a substantial frosty shower, my tent resembling a freezer that is in urgent need of a defrosting.  I measured -7.5C inside as I was getting up and dressed.  Yet my inner down bag was perfectly warm and dry, not even a hint of condensation.  When I got home later that evening the synthetic outer (which had defrosted) was saturated.  In my eyes the system had worked.

The problem with bulk and weight remains however.  In time for next winter I am going to order the lightest synthetic quilt that I can find.  The MLD 48 degree spirit quilt weighs in at 375 grammes for the extra-large.  It should marry up perfectly with my Hispar 500 for trips of more than two nights in the coldest weather.


25 Comments to “A two bag winter sleeping system”

  1. I’ve just been doing my accounts so all those gramme weight figures were making my headache; sure it was worth the weight though.

    Like your estimable self, I’d much rather carry plenty of warm gear and loads of food and be warm and full than be a cold, hungry ‘ultra-lite’ martyr. Why am I such a bitch? ‘Cos I just spent the morning doing accounts…

    When camping at – 20 in Romania I wriggled into two down bags with all my clothes on fearing that I’d be a rigid blue corpse in the morning otherwise. I was sweating my nuts off after about five minutes – live and learn.

    Haste Ye Back, Mr Boulter! P x

    • There are some pretty complicated mathematical calculations in this post Pete, that is why I did the sums for you.

      Don’t worry, I will resume my usual non gear related blogging stuff shortly………………..

  2. This is the system I’ve been using, too. A PHD down bag and MLD spirit 30 – if I were to buy the quilt again I would probably get the large size one. And I could use a warmer down bag, ideally. I have a micro-fleece liner for when I think it is going to be particularly cold, and when cold I’ll wear prism pants and and a sigma pullover as kind of backpacking jammies.

    • Good to hear that it’s a system that has worked well for you David. What sized quilt have you got at the moment? I thought about the extra large to give extra room for the down bag, but don’t know if will be too big (I’m 6ft)? Also can’t decide on 28 / 38 / 48 degree quilt – will probably only ever use it in conjunction with a down bag so thinking of lightest model…………….

  3. Yeah, it is for extra room when used with the bag that I’d like a bigger one. I got regular which MLD say is for 5.10 and under – I’m 5.11 but figured I don’t sleep lying completely flat anyway. It is actually fine at that size for just using by itself, and I really prefer using it than a bag now I’ve got used to it. 🙂 head and toe in event is probably a worthy investment, too (although I didn’t get it).

    • Aye, the head and toe in event is probably good but unsure if I would get it. I reckon an XL for me would be ideal for that extra room.

  4. I think a supplemental quilt is a good idea. Perhaps I should let you test the idea 🙂

    I’m not sure which MLD one to go for. Might plump for the 38.

  5. Good idea this James. I had similar thoughts awhile back, but I think you idea of having a quilt is better and lighter than a sleeping bag as the outer.

  6. whats wrong with a bivi bag.?

    i use a cheapy trekmates, weighs around 250grms (i think) gives extra warmth and keeps your bag dry. bonza !!

    • Hi Paul. A bivy bag is to protect you from moisture from the outside, I often use one when in my Trailstar, stops those drips. However it won’t prevent condensation forming on the outside of the bag from your body after a few nights in subzero temps. The idea is to keep the down bag dry and lofted.

      • thats strange, ive been using it for 2years now and had no problems. my summer weight bag is pretty hopeless unless its on a toasty european backpack so i pimp up its ratings with it. ive also used it this winter when it went well below -10 an suffered no dampness.

        i get what your saying it just hasnt happened to me… anyway you dont need to reply, i can imagine it can be quite tedious doing so as its off subject !

        oh yes before i forget as your a man of the doggy persuasion you might like my latest post.


  7. Have you thought about a vapour barrier liner inside your winter down bag? This will keep the moisture from penetrating the down. A lot less weight on a multi-night trip.

  8. Not a new idea. But Bags need to be made to match or the down will be compressed. Quilt idea is well used by Joe Newton and others in very cold conditions to make a light warm system. I sold my quilts on as on their own I found them no were as thermal efficient as a down bag. For me the idea works on long trips to help prevent down collapse. In very cold conditions a vapor barrier system also works – but stewing in my own juice does not appeal.

    Down is only as good as long as it’s fully lofted; heat is got in to it to be trapped. People forget it does not stop cold on its own. Plus an insulating mat is used to stop heat lose on the cold ground. For me mate invest in a warm 800g of down bag and sell the PHD one on. I was toasty warm the other night in my Alpine 600 with a winter pad. No clothing bar a base layer to stop my bag getting too dirty, and a ice coated shelter on a harsh cold night. Bit of food and warm up before bedding down, get heat into the down and then zip up for a toasty warm night. Lots things that all help, but also that MLD bivy I gave you over the bag will help keep the down safe as well.

    • Aye, aware that it is not a new idea Martin, but a new experiment in Bongo land sleeping comfort. The idea is for longer trips out in cold weather to keep the down bag from dampness. It really did work a treat in the Highlands over those four nights.

  9. Hi

    I’ll second David H’s view. I use a slightly knackered go lite adrenalin (rated -7deg – ha!) and the MLD spirit 30 (previous model, they have obviously expanded the range). I got the regular size with the eVent head and toe. If i purchased a quilt again I would get the larger size (to cover myself and the good lady, not because the regular is too small for me, or doesn’t work for solo – I’m 5’9 btw) and keep the event head and toe. I would def get the warmest rated one they currently offer, that way you can use it in british summertime on its own with a bivibag to reduce drafts. On very cold nights, I also sleep in a down jacket and my casadas, and some new primaloft socks.

    I need to renew my bag and my down jacket, but otherwise this system absolutely works. The footbox on the spirit is really handy, and the thing is light enough not to compress the down underneath. By day 4 of a recent trip the synthetic quilt was wet to the touch, my down bag was dry as a bone. It dries out fast enough, as most synthetics do. Only thing i’d say is all this slippery material means stuff moves around in the night, otherwise, it’s proven. It works, and more importantly, it works for multi day trips.

    • Sounds like that worked well. James. Funnily enough that combined weight is pretty much the same as my new winter bag that i bought just before christmas. I certainly like to be warm too!

    • Good to hear that this system works David. My outer bag was sopping wet after defrosting on the final night. Glad that it was not my down bag which was like that prior to using again in freezing conditions. I like the idea of using it as well to cover your tent partner, I’m sure that Reuben would appreciate that! (or Corrina if I ever get her out wild camping again…………..)

  10. When I was in Sweden and Norway earlier this year, I used a Rab Infinity 500 (-9˚C) and an old Synthetic bag (weight was not as much of an issue as we were cross-country skiing over relatively flat terrain). Temperatures hovered the wrong side of -20˚C but I was warm as toast. Got into my bag warm and stayed warm. It was lovely.

    • Wowsa, minus 20, doubt I would ever go that cold but glad to hear that the system worked for you Maz. One of lifes pleasures is a toasty bag on a freezing night.

  11. I treated myself to a new Rab Neutrino Endurance 600 for the trip (boosted by a complete change of dry sleeping clothes and fleece ski salopettes) . Weighs about 1kg and with a Thermarest Prolite sleep mat I was warm enough. Notice I haven’t used phrases like “toasty” ‘cos I was admittedly a little cold at times 🙂
    Mind you I was sharing a tent, no Brokeback Mountain jokes please!

    • As if I would make any innuendo…………………..

      A good mat always makes the world of difference. I took my bulky downmat, which is worth its weight in gold for warmth and comfort.

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