Extra large OVERBAG

[Moondog55]

I have just enough Lamilite to make a single layer overbag

http://wiggys.com/about.cfm

I know it will not be the lightest but I need to use the taffeta I already have for the liner; does anyone have any data on the best size and clearance needed for maximum moisture transfer from inner to outer?/
At this stage I plan to cut the outer bag to give about 10mm between my down bag and the overbag but I can cut a little bigger if need be.

The double bag will still fit inside my bivvy

[Moondog55]

Well I now have only 3 weeks left to work on this project and I haven't even started.
I have been looking at Big Agnes bags and the way they use a sleeping pad ( very much like the old macpac marathons but with full sized foot box) and thinking perhaps that cutting the overbag with a flat bottom and adding an extra layer of fabric for a pad sleeve or using tape to do the same job may work better, this would allow a double layer of insulation on the top.
PHD use a single layer of Thinsulate on the bottom of their overbag with a double layer on top.
BTW Lamillite is the same stuff as Climasheild and used to be called Polargard. I have the 5oz stuff about a centimetre of thickness.
I was going to buy the PHD overbag but remembered I had this roll in the garage which I bought for making a belay parka and then recycled my old ski parka for that purpose

[Nuts]

I'm not sure I understand, the size of the overbag would be determined by the size of the inner bag (assuming it cant be opened quilt style (but then there wouldnt be much purpose using it for cold weather as an 'over' bag) ?

An idea:

I recently made a quilt, kinda overbag bivy 'thingy' (im not sure exactly what to call it I just had function in mind).

I wanted a summer quilt (used with a silk liner) that could also function as a overbag in winter. I wanted it to be versatile in being able to do both jobs, on its own, mat inside or out, using a bivy (or not).
Anyhow... (needs a linelock at the top and a bit of tweaking yet), a pic may explain:

It has enough size to pull in under (has a single drawcord, drawn from the top) or be big and flat (with no zips or openings), just an experiment, time will tell..

PS weighs abt 400g's but a nylon (or something) floor wouldn't add much weight.

[Moondog55]

Thanx Nuts
I was making an assumption that there should be an "optimum," size for an overbag, rereading the PHD site I think I am mistaken, their overbag is sized for the largest bag in the range, so the next part of my question is--- Do I make with a flat base or a tailored base and do I add an extra layer of nylon to act as a sleeve for an extra wide foam mat?? or do I just use lightweight tape ?? For winter I prefer a 600 wide pad even though those are much more expensive, and i will use the Thermarest or DAM on top
I have never camped in minus 35C temperatures before and just want to make sure I "GET IT RIGHT' first time

[Nuts]

No, ive never camped at -35c either. I think you have the right idea, synthetic overbag. Climashield though is thicker than that, I used 2.5oz and it would be over 1cm loft...
Is the only purpose of the sleeve/straps to keep the mat in place, wouldn't the bivy do that?

[Nuts]

If I had the skills to keep the size right i'd make a overbag to mimic the dimensions of the inner bag personally, keep the mat 'floating'. If its in a bivy wind shouldn't rob the heat. You'll probably need to use clothing in the system or hope that you dont get too may warm nights? Good luck

[Moondog55]

Fair enough Nuts.
I'll try and make it a mummy or semi mummy style then. I may then modify the Foxhole to take the extra wide mat underneath, some silicone will fix the stitching penetrations there.

[Moondog55]

Climashields weight is the weight of the insulation only; Lamillite weight is the weight of all 3 layers, the insulation plus scrim ( which is practically nothing) plus the outer shell fabric, which in this case is 2oz per square yard Taslan.
I got this stuff from a maker of military sleeping bags and this is what they were using for their overbag, except they were using 2 layers of this as inner and outer, can you imagine the total weight of the armys full system??
Years ago the Army used a Paddy Pallin Bimberi for special forces troops and it was a good bag but woefully inadequate for winter in the snow

[Moondog55]

1tonne tape on the outside

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1tonne tape on the outside

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Detail

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Inside detail showing half tonne tape and taslan reinforcing

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Foot end, added the tape just after the Goretex section

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Well I just spent half an hour sewing tape into the bivvy sac to hold a winter Closed Cell Foam mat.

[Nuts]

One tonne tape lol.. you don't do things by halves lol.. I think i see, you have one mat outside, one inside. I have found that the CC foam feels warmer on top, not sure it makes much difference.

[Moondog55]

One under; mainly to protect the bivvy bag if on rocks etc; inner as well to stop the pad from slipping. the tape is what I happened to have on the shelf but I thought to m'self "What if I need to bivvy in a precarious place" and so I used something I could tie off onto, good enough for most situations I would find
myself in.
Also using the 55mm wide tape spreads the load over a wider area.

[Nuts]

right... good thinking.

[Moondog55]

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Well I have started pinning the overbag together.
i am begging SWMBO for help with this one as she is experienced in sewing quilting.
going on the advice in Gerry Cunninghams book I have cut this 7inches (185mm ) bigger around than the down sleeping bag, this is going to make it a very tight fit in the bivvy sac and I may have to trim it a little.

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The longer this is out of the package the more loft it has, now almost 25mm thick

[Moondog55]

Got a bit more done over the week-end.
Pinned over the top of my combination and played around with the fit.
I want and need it to be big enough but not too big of course.
A single layer of this stuff is reasonably warm, much warmer than the single layer of thinsulate in my cheap summer bag.
I think this is going to work out quite well, if I give it a DWR treatment I can make a decision on the day as to what emergency shelter I pack, either the Goretex bivvy sac or the Megamid

[Moondog55]

What is the "BEST" hood shape for this type of bag/ the simple rounded cowl and drawstring or something with more shape that would envelope the head ?
I am sewing the foot of liner with an extra layer of the 3M reflective insulation as well, not so much for its insulative qualities but because the stiffness will hold the foot of the overbag up and not compress the 900 loft down filling of the mummy bag, I am using a heavily resinated ripstop as the foot panel for the same reason and paying the 10 gram weight penalty.

[Moondog55]

I have decided to do it with a pieced 3-Dimensional hood, top layer also has the 3-M reflective insulation; again more for the little added stiffness but 2mm of extra thickness on this area won't be wasted

[Moondog55]

OK just checking now that everything will layer up.
Inner lining is cut out and pinned, we have a week left until the flight out and this will be finished in 2 days

Total loft 370mm cold, it increases as the down warms up
And they all fit inside the MD "Foxhole bivvysack

[andrewa]

Heh, Moondog, I'm having trouble seeing what you're doing with your overbag.............!

I can see the pink crocs, and the scales......

(I'm presuming you've "bumped" into the Army guys in camo gear at some stage in your life, and said "sorry, Mate, I didn't see you.......).

Clearly you've been on a busy/manic phase, as I have, but mine has been RED.

Have a great time away. I hope it is cold enough for all your gear!

Andrew A

[Moondog55]

I used to wear a slightly different pattern myself LOL
All I can say in my defense is that the fabric was cheap.
I was told to expect minus 30C and colder and they are having their mildest winter in over 150 years, but I know if I leave the skis and extreme cold weather gear behind the weather will change as we hop on the plane

[Moondog55]

FINISHED
And only just in time as we fly out tomorrow morning ( Xmas eve ) and it looks like it won't be needed after all.
Warm for the time of the year, no white Christmas for us.

I learnt a few things making this, for one I need a new sewing machine with a high lift and a walking foot

[andrewa]

It's good to have a Christmas wish list!

And it will get colder.....

A

[Moondog55]

I will take photos of this gear in use.
you will just have to wait 6 weeks or so for the trip report

[Moondog55]

OK i am home and sad to say there was very little snow and it was warm.
The coldest nite was only minus 17F ( -24C) and i did not need the down bag or my big down parka.
this kept me warm using my lightweight footsac and a layered top half, in fact I took off the balaclava about 1AM as I was too warm.
my top layers were silk weight long sleeve, old polartec 100 shawl collared top, merino jumper and my softshell/Puma tracksuit top.

Critique ? just a little too big, and the outer fabric is weather proof enough not too need a bivvysac if rain isn't in the offing, I could have saved a kilo in my pack by leaving the Foxhole behind.
As a proof of concept experiment I am actually very happy and satisfied enough with the results to either do it again in a lighter weight outer shell or just order the thinsulate overbag from PHD

[Moondog55]

I have been thinking more about this overbag, and the whole double/triple bag concept.
one way to save weight would be to resurrect Gerry Cunninghams idea of the "Mountain sleeper" which is where I am sure Big Agnes got their original ideas from.
By cutting the bottom from the bag and using a double layer of silnylon fabric in a sleeve to hold a sleeping mat I can reduce the packed bulk by a substantial amount.
the only trouble is I would probably need to put in a decent zipper and I am poor at retro fitting zips ( woeful in fact )
Easier to start over with a new project, so looking for input on fabrics and insulation, weight and minimum packed bulk in a synthetic fibre.