Goretex bivvy inside the insulated overbag second query

Discussion in 'Sleep Systems' started by Moondog55, Mar 26, 2017.

  1. Moondog55

    Moondog55 Guide

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    So I'm asking again in a new thread rather than trying to raise one from the dead.
    I am prpearing all the gear I will need for my bucket list trip in a couple of years.
    I need to boost the temperature rating of my sleeping system to cope with -40 and lower.
    Becuase I will only need this combo for a single trip of about 90 days I see no point in buying a single good bag that I will never use again and what I own is really close to state of the art.
    This is a specific query about using my existing system including my Goretex bivvy bag.
    System as it stands is my old Everest summit assault bag; expedition cut to fit over an XL sized down suit, rated at -4C on its own under the usual test conditions. Inside that I use a Western Mountaineering Tamarack short sleeping bag rated at -2C and a down parka insulated with a full 600+ grams of 650 FP DryTek down.
    When using a snow cave/snow hole/single skin tent I have an XL Full bivvy that goes over everything.
    This combination is good down to -30C easily, it is a sauna at -18C/0F.
    What I cannot experiment with over here is using the Goretex inside the very big synthetic overbag. it simply does not get cold enough ad OH&S and insurance will not allow anybody with a big blast freeze to allow me to test.
    Using 80GSM synthetic insulation in the overbag I am trying to determine at what temperture the Goretex stops allowing vapour to leave the inner bags
    This is second generation highly breathable Goretex specific to bivvy sacks and was never used for jackets as it is not waterproof to 10,000mm, even though it does keep off a decent rainfall.

    If 80GSM won't keep me warm enough I cn add more insulation when I convert the overbag form its current style to a Gerry Cunningham Mountain Sleeper with an integrted sleeve to take the full mattress system
     
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  2. RJM52

    RJM52 Scout

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    Having used two different GoreTex bivies, my belief is that if you put the GoreTex bivy in between your inner and outer bags you are going to turn the inner bag into a sauna...

    I love GoreTex as it is lightweight and waterproof but I don't kid myself at all as it to it being "breathable". I buy my GoreTex rainwear two sizes lager than my normal size so it "breaths" by being loose.

    Bob
     
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  3. Moondog55

    Moondog55 Guide

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    Thanx Bob I know may people seem to think this and have this problem but have you ever actually tried it?
     
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  4. RJM52

    RJM52 Scout

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    No but the last two times I slept out without a tent in just a GoreTex bivy, one military and one Kelty, there was frozen water vapor on the inside of the bivy.

    Now if there is another sleeping bag over the bivy the water vapor will not freeze but neither will it escape from the bivy....and lets say it does. The bivy will act a heat barrier to the outer bag and any moisture that did get out of the bivy will freeze in the outer bag...especially at the temperatures you are talking about....

    If you are going into -40 conditions I would suggest you read some of the articles about polar explorers who have used down and the problem with water vapor/ice buildup inside the bags over a short period of time...
    Bob
     
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  5. morganbw

    morganbw Scout

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    Forgive me, but if you are planning a 90 day trip at -40 degree/C or F. You need to make sure your gear is geared to even a lower temp.
    A 90 day trip is an epic event, please do not go short.
     
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  6. crewhead05

    crewhead05 Supporter Supporter

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    A couple things. I agree with @morganbw that if this is a 90 day expedition buy the best you can afford.

    If you are in your bag every night its going to accumulate moisture if not given the chance to air out. Keep that in mind. Though I havent tried it, I think you will be negating the insulation potential of your outer bag if you have the gortex bivvy in the middle and you will be dealing with more moisture on the inner insulation than if you had innerbag/ outer bag/ and bivvy.

    I did 4 years in Alaska as an infantryman. The USGI 3 bag system is legit and we often used them in the temps you are talking about. (Remember the thicker bag goes inside the thinner bag). Also if you put a air mattress/ insulating pad in your bivvy it really helps with heat loss through conduction.

    A final couple thoughts. See what the guys you are going with are using, ask questions of the more experienced ones, they will hopefully set you straight. If you are looking for a good sleeping bag system that wont cost an arm and a leg, Wiggys bags are my recommendation. http://www.wiggys.com/by-temperature-rating/ The insulation he uses, in my opinion, is some of the best you can have for keeping you warm while moist from many days of back to back use.


    Good luck on your adventure and I hope you post lots of pics!
     
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  7. Moondog55

    Moondog55 Guide

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    It is several trips over my 90 day stay [ 90 days is the longest I can stay without paying megabucks for a visa ] but hopefully I can spend most of that in the outback
    Crewhead my overbag is made using fabric frm Wiggy; honestly it is pretty basic stuff, very far from state of the art being cheap generic polyester batting much like the MSS issue system bags, a little thicker than the green patrol bag, it doesn't compress much which can be a good thing in an overbag.
    I do have an MSS bivvy and patrol bag tho for comparison, my mountain bivvy sack is just a touch smaller than the MSS bivvy but longer, my overbag is big enough to go over the regular MSS system
    RJM if the frozen condensation is inside the bivvy I have a problem but if it is outside the bivvy on the overbag I'm going to be happy, this is what I am trying to get an answer to, how much insulation do I need in the outer bag to keep the moisture inside the down inner system as vapour so it will pass through.
    none of the fellers I am going with have ever used mountaineering oriented gear before so they have no frame of reference.
    One of the reasons I need the extra information is that while I know it is warm enough for a few nights on Everest it may not be warm enough for more than a few nights on Denali.
    Here is the google link to the pix of the system I want to modify
    https://plus.google.com/photos/104496919004974772120/albums/6175249196020753585
    I have used that particular overbag on Wolfjaw at -25C without the big sleeping bag and duvet and I was warm enough to sleep 7 hours, using a Chouinard Megamid to block the wind but I was wearing every other single other layer of clothing I had with me
    I know one of the solutions is to make a VB and use a LW down inner bag and keep the down parka for day use.
    Before my last trip over I did have another thread where a lot of these issues were discussed but the issue of using the Goretex inside the over bg was never satisfactorally answered
     
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  8. Moondog55

    Moondog55 Guide

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    Just in case any of you think I am unprepared for this trip I assure you I'm not.
    If I have to I can use my big linebacker overparka to boost the insulation over my foot and leg area and the insulated winter poncho over my torso as advised by Garret Conover and the Winter trekkers.
    Poncho [ like the linebacker overparka ] has 100GSM of high loft polyester lining just like a Doobie but I made it using the German cotton poncho because I may be wearing it around an open fire
     

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  9. RJM52

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    "RJM if the frozen condensation is inside the bivvy I have a problem but if it is outside the bivvy on the overbag I'm going to be happy, this is what I am trying to get an answer to, how much insulation do I need in the outer bag to keep the moisture inside the down inner system as vapour so it will pass through."

    As crewhead said, I also think by putting the bivy inside the outer bag you are not going to heat the outer bag...

    I'm also a Wiggy's fan. The coldest I've ever been in his bags is zero but only had his fishnet underwear on...I am not a clothes sleeper....

    Bob
     
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  10. Muskett

    Muskett Tracker

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    Goretex can breath but its not good at breathing unless the conditions for it to do so are correct, cold outside with airflow, and warm inside. EVent fabric is slightly faster, or maybe some newer special goretex. But without the inner and outer temperature difference neither do much, or just not fast enough to cope.
    When sleeping you produce a shed load of water, start the night overly hot and then even more so. Unless it can travel away with air flow it will stay put, or condense on the first cold surface it hits. Once no longer steam and real drops of water then its not going anywhere. If it pools then it encourages more pooling until a puddle. Best if that is the outer inner of the tent not in your sleeping system.
    So wherever you put the goretex/barrier it should be on the outside, or as far out as you can. Or non at all.
    (Air kit as often as possible while it still has some heat in it, to rid the moisture for the next night or the moisture will accumulate. First night might be fine in a steamy sort of way. Second night the moisture doubles up and things start to get wet rather than steamy. Third night its a puddle, thats if the bag hasn't frozen up).

    Warmth is held in by loft. The more air trapped the more loft, the less escapes before being replaced from natural body comfort heat. Naturally pumps itself away outwards. You want a slow gentle trans flow out, all the way out. Too fast then its cold, so the trick is how to get it right. How hot do you sleep as everyone is difference? If using multi bag systems then each outer bag must be large enough not to compress the inner bag. They must also let the transfer out without becoming a barrier.

    Tents are protection from the wet and high winds. But as important can provide an internal climate and gentle airflow for your sleeping system to work. The trick is to keep the interior of the tent a good few degrees lower than inside the sleeping bag, but not freezing cold. A candle or water bottle might do that, for a while at least.

    In truth I am getting out of my knowlege. Those with more experience than I battle to find a solution. Specialised kit can sometimes be the only solution; and thats at its limit too. In the cold its all about moisture control, by stopping the steam turning into wet.
    One hint I'll give, get used to sleeping with cold outer air. The worst time I had was just after when first married. I'd had six months in a hot bed and hot central heated bedroom. Flippin nearly froze, just not ready for the change even though I was using my tested kit.
     
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  11. Moondog55

    Moondog55 Guide

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    I was hoping that some-one with similar kit to mine had already tried this method and could give me feedback. I guess I'll just have to wait and try it for myself.
    The bivvy bag only weighs 700 grams so no real burden compared to the 1600g of the overbag
     
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  12. Muskett

    Muskett Tracker

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    For these extremes I would stick to the tried and tested. Its not the time to experiment. Local knowledge goes a long way (locals can be hardier) or contact someone who has been there before. Compare notes. Maybe its less to do with just packing on more insulation and more to do with controlling the environment... heat source to the tent. (Doesn't take much to heat an igloo).
    Lastly, as I'm not really helping here, don't forget to upgrade the sleeping mat; as there is nothing worse than sleeping on a heat sink.

    I've extensively used bivi bags but not down to those negative temperatures. At -30, -40 things start to freeze fast and its a different game altogether. At least the air is dry. Whatever you are up to it sounds fun.
     
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  13. Moondog55

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    Thanx Muskett
    I'm good to negative 30C easily, as I have said before it is that next step that bothers me.
    I've been communicating with the WinterTrekkers and no-one has tried this experiment [ also it has been a warm winter] even tho a lot of them do use bivvy bags t these temperatures they use them more as protectors for the SB and shake out the accumulated frost in the AM
     
  14. Moondog55

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  15. CHREBA

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    I'm very interested in this . While not even remotely considering any thing this epic . I've tested my EB Kokoram bag with just the GI bivvy and a insulated pad inside the bivvy on top of a all weather blanket shiny side up . With a Bear Suit and wool hat with a full face baclava for clothing and had to unzip it was so hot for me I felt stiffled at 12 below with unknown wind chill temp . I've never experienced -40 but I cant see where that temperature difference would require a huge amount more IMHO . But in all fairness I'm a walking sauna anyways . But as I said I've never experienced that type of cold anyhow . Just for the record I'm literally on the south shore of lake Ontario and this was during a Noreaster . I had ice on the outside of my bivvy .
     
  16. Moondog55

    Moondog55 Guide

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    I'll do an update of course when and if I get the chance to
     
  17. lobo9er

    lobo9er Scout

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    maybe theres a reason no one has done this. just my take away and I mean no disrespect, you are gonna go on a bucket list trip to -40 temps and take a hodgepodge sleeping bag system? I have no experience with that type of trip but if it were me I wouldn't skimp on warm weather gear in that situation. I've only goofed around at cold weather camping one weekend trip and the rest in the backyard and have found being cold is miserable.
     
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  18. lobo9er

    lobo9er Scout

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    +1 for checking out wiggys offerings
     
  19. Moondog55

    Moondog55 Guide

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    Ho Lobo
    Not sure why you are making the assumption that what I have is hodge-podge or inadequate in its own right, it is good enough to summit Chomlungma [ Everest] in; it is even almost warm enough for Denali
    Have you not heard about One Planet gear? OP make the gear Australians use in Antarctica
    But you are totally misunderstanding my query.
    By the way I have one of Wiggys overbags [ The Australian Army tried them as an experiment] and quite honestly it is junk. Heavy and not really all that warm, cheap generic polyester fill [ it is not APEX; it's Climashield cheap stuff] and fabrics that are too heavy and compress what little loft there is. Also I used the Wiggys fabrics to make my own overbag using surplus from Crossfire Wiggys Australian outlet and maker here
    OK if I was car camping but no way adequate for sled hauling and one of the main reasons for me asking ths question
    Are you trying to tell me that Western Mountainering bags are also inadequate? Because the Tamarack from MW is my half bag on my legs and torso
    Please go back and read all of the thread
    I can DIY if I have to and I enjoy the effort and time spent and it then becomes my own responsibility to get things right but I do not like working with down
    All I wanted to know and needed to know is if anybody has tried what I propose
    Also I have an MSS, I do not use the inner black bag at all anymore tho, too heavy by far, a cheap down bag is warmer and lighter by a half kilo
    My own system is warmer by at least 10 degrees and half the weight but it is not warm enough for comfort at -40 at my age and it is too big in itself to fit inside the MSS shell and patrol bag combo or I would have considered that
    You need to take into consideration that comfort at -40 is survival at -55 and the comfort rating om own bag system is without using any of the normal adjuncts like using your big parka as an extra layer but it does assume wearing light clothing like socks and long-johns and a warm top with hood.
    Check the photos
    That sleeping bag has a full 150mm of loft, the duvet parka has 100mm in the torso and 50mm in the arms, one fits inside the other. It is a climbers bag system
     

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  20. lobo9er

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    Its actually climashield "combat" the same stuff kifaru used to use before "apex" came about is what I found out about lamilite. But I admit you probably have more experience than me. Your first post in the second paragraph you list several separate independent items you use together to create your own sleep system, and I apologize for the term hodgepodge as it may be a mixture of items, but it may whole heartedly be perfectly adequate for your adventure and furthest thing from a hodgepodge mixture. To go back to your OP I would buy a system or singular bag from a company you trust and made specifically for what you are doing. 90 days with the possibilities in -40 and its your bucket list trip, money spent on your sleeping bag will be a minor detail to the story after your trip. The other suggestion from muskett of asking the locals is probably the best advice in this whole thread. People who live in those conditions is your best bet. Covering your current set up in a bivy and then another over bag, I have never heard of that tip or trick anywhere so far but maybe its a great idea. I wouldn't try on your trip first though. I hope in 2 years you post the details of your trip it sounds like an adventure.
     
  21. hunter63

    hunter63 Bushmaster

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    Sorry....
    Come to my mind that if this was a workable plan...some one would have used it and answered the question.
    You can ask it as many times as you want....but would need to "try it out" to be sure.
    You are looking for people to agree with you....so far no takers.

    No one want your bucket list trip to be your last trip
    I vote No bivy on the inside.
     
  22. Moondog55

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    Actually No I wasn't
    I was and am looking to see if people have tried it and if so how it worked, one way or another. I know from personal experience that this old Goretex works and breathes well enough down to -25C where the frost simply shakes off the inside in the AM

    I am quite willing to "Try it out" when I get there to see for myself but a kilo is a kilo and IF it wasn't a viable option I'd simply save the extra kilo and bring the huge insulated shell anyway
    So far all I have had is opinions and while they are valid concerns on the part of the posters it seems none of them have read the question as I wrote it, that is "Personal Experience"
    I'd be happy to go sleep in the local blast freezer if OH&S rules didn't scare the **** out of all the local warehouses
    Owners and designers at OP are not willing to give a definite answer either just a "Maybe" as they field test all new designs down South and have no need for very cold test facilities and they do not use WPB fabric for any of their SBs; we are now such a litigious country that honest advice is hard to come by.
    I could buy a Snowy Owl from FF but I'd have to sell at a huge discount when the trip is over and I'd rather spend that money on other things such as paying the locals for their guiding experience and snow mobile hire etc
    I had a mate in Connecticut who was willing to give it a trial but it simply never got cold enough where he is
    I've just been to the Big Agnes page on one of the overbags I was initially thinking about
    http://www.bigagnes.com/Cross-Mountain-45_2
    And the over bag advice they used to have there is gone
    Same for the Summit Park down bag
    http://www.bigagnes.com/Summit-Park-15-600-DownTek-LONG

    We all know that using a synthetic outer bag/over bag works and I would try it out here but it simply never gets cold enough for me to use my Everest bag combination here without sweating
     
  23. hunter63

    hunter63 Bushmaster

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    Good luck and have a good time on your trip......
     
  24. Moondog55

    Moondog55 Guide

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    OK I'll back step and look at getting a newer big bag then just in case what I was planning will not work.
    I also asked this over at Wintertrekking and answers there were also mixed but no-one had the opportunity to try on my behalf.
    What is the collective opinion on the Western Mountaineering Kodiak sleeping bag/ the bag is a little bigger all around than my current one and about 12 degrees warmer. This is not too warm to use here in an Australian winter when ski touring or climbing in a New Zealand winter and that is the 10 degrees I need.
    http://www.westernmountaineering.com/sleeping-bags/microfiber-series/kodiak-mf/
     
  25. wizard

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    While I no longer have an area to test such a setup. I can say that my experience with Gore-Tex bivy bags in below zero conditions have resulted in my sleeping bag being frozen on the outer cover, just inside the bivy. I would look into a inner VB solution that would keep all body moisture away from the insulation. Much like Chouinard used to recommend for footwear. light poly sock, then the VB sock, heavy wool sock then boot.

    I have to agree with the concept of going with the best option, even if it means purchases must be made. There is no way I would attempt weeks in -40 with a questionable system. How are you moving this system around? Certainly not carrying all of that in a backpack or on a pulk. While that is all I have ever done with cold weather gear for mountaineering. The gear I take has to be more portable and not require a 5-ton truck to haul. For a Denali trip the sleeping bag I chose was the TNF Dark Star -40 version. I know they still make that bag but not sure how much it has changed since my 1998 version. My choice was made by overall cost and functionality. I figured a synthetic was more durable in the conditions, dried more easily and was somewhat expendable.

    While I know many here love the Wiggy's product, I see them as way too heavy and bulky. Fine if you aren't packing it on your back but otherwise way too heavy. I also do not buy all the hype they profess to market their product, it is not a miracle fiber, just off the shelf insulation with a proprietary name and nothing particularly magical.

    I would trust Western Mountaineering products, they have a stellar reputation and are highly regarded by everyone. They are pricey but live up to their quality reputation. BTW, the one I would be looking at for -40 conditions would only be this one http://www.westernmountaineering.com/sleeping-bags/gore-windstopper-expedition-series/bison-gws/ Too costly for my taste. I'd still go with one of these http://www.trailspace.com/gear/the-north-face/dark-star--40/
     
    Last edited: Apr 27, 2017
  26. Moondog55

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    I regularly haul 90 kilos in our wnters for the basecamps and 35+ when touring
    Some extra weight for comfort I can put up with when the distance isn't so great. I an not going to Denali as I am too old and out of practice to even attempt that.
    The reason I am looking at a -18C bag rather than a dedicatd -40 bag is that -18C/0F is a very reasonable T=comfort for Australian winters and doubling up is a cost effective method of getting the extra 20 degrees needed.
    I'm still reasonably skinny and that Kodiak is plenty large enough to fit a second bag inside it without crushing the loft of either.
    One Planet here have offered to sell me at cost one of their Antarctic overbags for me to use but at 2300 g they are similar to a Wiggy bag and too heavy for me to contemplate. Also they have a dedicated zipper system similar to the MSS and work best with the OP Antarctic sleeping bag. I may get one or two tho for car camping as they are rated -12C on their own.
    If I do use a goretex bivvy over a down bag and then the synthetic overbag my initial thinking was that the water would stay vapour and condense inside the outer protective layer, the synthetic being so much easier to dry than water resistant down.
    One of the reasons for the huge weight in my initial posts is that some of the folk I will be trekking with are hot tenters and they use wood stves and canvas tents and have told me I need to shoulder some of my share of the communal gear.
    Otherwise I am going to do everything I can do to get the weight down as low as practicable and reasonably safe
    I do find it interesting tho tht you are saying not to use a Goretex bivvy sack but recmmeneding a sleeping bag with a Windstopper shell when both are functionally the same
     
  27. wizard

    wizard Guide

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    The only bag I can say I recommended, from actual experience is the TNF Darkstar. The one I own has poly ripstop, not windstopper or other breathable/water resistant fabric. I have found a difference though between a down jacket in Windstopper and a regular down jacket under a Gore-tex shell, same concept. I do see your reasoning on the -18C bag and hope it all works out for your plan.
     
  28. justin_baker

    justin_baker Supporter Supporter

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    Why are you trying to sandwich a super low air permeability layer in between two sleeping bags? What are you trying to accomplish by doing that? Even if using a vapor barrier layer I don't see how that would add a significant amount of warmth in addition to the mountain of puff on top of your already.
    Also, where did you find a 600 gram down parka? That sounds insane!
     
  29. Moondog55

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    G'Day justin
    Well at the moment I don't know if it would work but theory says that the exterior synthetic bag should keep the surface of the Goretex above the vapour point of water so the down bag would keep dry and the frost could be shaken out of the outer bag as regular daily maintenance. If this worked then there would be no VB liner inside the big bag.
    I've had the duvet for decades, I know it's old school but personally I have found that 650 FP down is far better for clothing because it doesn't suffer so badly from wind compression.
    Duvet parka was made by the Australian company Mountain Designs back in the days when it was owned and run by a climber and not a bunch of accountants. Parka weighs 1100 grams with the cod-piece and ~600 grams of that is down, there may be a little more down than that but certainly not less, it is overstuffed by design. Was built for Everest but I never got to go, family and kids and all that, it's why I have the super light summit assault bags etc. It came with a Thinsulate insulated Gore Windstopper wind suit top, ditto the down pants but I sold the pants and windsuit to another climber a long time ago.
    It is a climbers parka, slim cut arms for using tools like ice-axes etc and a lot of insulation around the core, fully box walled, inch high baffles I added the insulated cod-piece myself to stop it creeping up when sleeping in it and when climbing in cold weather it protects the loved ones well as an added bonus.
    It was sold as and effectively used as a -30C suit for high alitude climbing, I guess the parka would be good for -30C on its own for light to moderate work.
    I've slept in it using the half bag and the bivvysack at -18C and been warm enough to get 6 hours
    25+ years ago the parka cost me about $350- I guess as part of a $2k Everest suit and the sleeping bag was about $600-, that was a lot of money in those days, I think the Foxhole bivvy bag was almost $200- at the same time. it was quite a long time ago and I'm a little fuzzy on the actual costs after all this time but good gear lasts and it has always been stored correctly
    I just took a tape and measured around the chest of the parka because it is hanging behind me, it's 52 inches around the outside of the chest and total girth is 65 inches and the sleeping bag in the picture has an internal girth of 65 inches I only just fit in but that means very little air pumping and no excess space to warm up, if I was wearing the windsuit I could not do it, i'd not fit inside.
    Parka was sized when new to go over two layers, expedition weight underwear and a polartec 300 fleece, these days I can only wear the underwear layer due to the dreaded spread
    Any more information you want just ask, I'll try and remember
     
  30. Moondog55

    Moondog55 Guide

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    Well our winter and ski season is fast approaching and my annual camp is on again.
    Even tho I'll only have mild overnight temperatures I think I should take the time to test out the idea at -12C, I'll put the overbag over the MSS bivvy&patrol bag combo for a few nites and see how much it effects the vapour transmission of the goretex bivvy. I'll wait for a cold frosty clear night and do the test outside the tent
     
  31. Moondog55

    Moondog55 Guide

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    Well I did get away for a week-end but so far this is a very warm and dry winter and it never got below freezing even above 1500metres although there was a hard frost. The overbag had frost on it but the goretex bivvy was dry although I'm sure this isn't any indication of what would happen at -30 or lower
    I know I was cold during the night using just the US bivvy+ patrol bag + the overbag and had to put on my pants and jacket about midnight.
    I thought about what everybody has said and I've ordered a quilt from Nunatak to go over my big bag.
    It will take at least 12 weeks to build as there is a long queue for custom work but the result will I hope be worth it
    I ordered the widest they make and 80 inches long with a 46 inch around hemispherical foot and a 26 inch wide uninsulated pad sleeve and 3.6 ounce filling. Supposedly go0d to 40F on its own
     

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