DIY synthetic overbag; design queries

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Moondog55

Forager
Sep 17, 2023
116
48
72
Geelong Australia
I might get around to sewing some stuff up again soon; just because I have the materials here and I'm a bit bored.

While I'm happy enough with the new Halite overbag for milder conditions and it seems to work very well with my UL down inner it is sized for Regular sized mats.

I want to make something that works better with Large sized mats.

Been rereading Jerry Kobalenkos web pages and noting his overbag uses no insulation on the base and has a centre zip and a round face hole in the Eskimo style, while other makers like PHD in England use the nominally standard side zips and simple cowl hoods and a few others such as Halite and Helsport use dual zips on top but to either side of centre and shaped col hoods .

The last one I made was a simpler wriggle in style both because it was easier and my winter sleeping bag was also a simple wriggle in style. I still have that bag and while superbly warm is is now a tad tight if I want to or need to wear a big down jacket inside it and I'm thinking I might buy a new winter sleeping bag and I am still dreaming of Denali.

Ground level side zippers would be the easiest to sew up, with a synthetic APEX top [ I would lightly insulate the base with a layer of Thinsulate] bother other styles of zipper would probably be of equal difficulty but dual zippers would cost more naturally and take twice as long to accomplish.

Any Arctic wanderers here able to assist in the design process again?

The last time I asked similar questions got me to order my custom overquilt from Nunatak which still works very well down to Australian low temperatures but was only designed as a 10C boost and without a hood, this time around I am thinking of thicker insulation and a 20C boost would be needed. I have a section of 3.6oz APEX plus a section of 2.5oz APEX and I'd use them laid at right angles to each other.

If I do make this up the new sleeping bag has a LH zipper and is rated to -4C for comfort [ this is female/ cold sleeper rating] but I'd order an extra 150 grams of 850FP down to boost that to ~ minus 10C and at 178cm inside girth there would be enough room for me to wear my down suit inside it.

Although there is an alternative sleeping bag from Macpac that has much less zipper but is cut smaller so I can't wear a big duvet inside it.

Or another alternative is my old Everest summit bag [ which never got used due to the totally unexpected arrival of a child in the family and not being able to afford both a daughter and a trip to Everest] which is good to about -18C

If I do ever make it to Denali I'd definitely be buying a new down LW suit and parka.

I've been using my custom Nunatak overquilt for a decade now and it isn't quite as warm as it was when new although still functional I'd guess now it's only a 5 C boost.

I have one of the Halite Overbag Lite but it is so small I can only fit a summer weight bag with 300 grams of down inside it with the S2S Comfort light mat in Regular size.

So I am thinking I need something like the Halite but sized to fit a Large mat.

The questions are 1: what hood type works best for cold weather>? A simple shaped cowl with drawcords or a heavily shaped Eskimo type with a round opening?

2: is a single zipper warmer that twin zips but are twin zips more functional and worth the extra time, hassle and expense?

3: How much bigger should an overbag be to give the best bang for added dead air space between the sleeping bag and the overbag?

4: Is it worth adding in a LW delrin hoop at the foot end to preserve dead air space over the foot end and minimise compression of the inner bags down loft?

I should point out that I'm a biggish bloke, 184 tall and I've got fat over this last decade and now mass 115 kilos and my waist size is almost equal to my 117cm chest

Has anybody got a pattern for an Eskimo type hooded sleeping bag by any chance??

I have fabrics and I have both APEX insulation and some 3M LiteLoft as well as lots of double scrimmed 40GSM Thinsulate
 
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Moondog55

Forager
Sep 17, 2023
116
48
72
Geelong Australia
Well hopefully.
I've made a few bags myself and none of them have been quite right and I really need some help. Integrating my big mothership parka into the sleep system is perhaps one of the partial solutions so I can use a lesser weight of insulation in the overbag but deciding where to use it? Inside the overbag or simply buttoned on top?
Also depending on where I might wind up if I manage to save enough money for travel might make a difference, Canada and the yearly Operation DeepFreeze off the PolarBear Express rail line and hot tenting will be very different to a lightweight manhaul trip in Alaska and Denali would be different again; and I'd like to cover those options with minimal changes.
Two parka options, I have an L-7 Linebacker US surplus and a DeadBird LW synthetic belay.
The surplus option is warmer but twice the weight and bulk of the smaller Arcteryx Nuclei
 

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