Bag idea???

Aaron,

How long does it have to last?

What size do you want it to be?

Aaron,
Do it. That's the only way to know.
1) Down plumules will not penetrate the Primaloft, but some quills may. But that won't matter; quills don't insulate.
2) Yes, the PL on top may limit the loft of the down somewhat. Any weight on the down will tend to compress it. However, if you use a 'space filler' cut for the inside fabric, the down will loft downward, and the weight of the PL will not be much of a problem. To achieve a space-filler cut, just make the bottom shell the same width as the PL. That should work out OK.
3) Have you considered using only PL? You can get to 32F pretty easily with PL alone. With PL and, say 1.5" baffles for the down, you may have more insulation than you want. You might want to play with the insulating capacities of PL and down to figure the optimum.

Bill,
Oh thanks, so now I'm in the disposable gear making process. No, this is not for the JMT attempt.
I could always use some fabric backing to hold it all together.
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Vick,
Right now I'm still in the R&R development looking for some highensight.

Size:
I rarely move when I sleep.
The bag will not be separate, it will just have separate sizes from top to bottom of the hands and bottom on down.
Top will be 40" X 45" (W-H)
Bottom tapering 32" to 24" X 45" (W-H)

This gives me 3060 square inches and 5 ounces for the fabric.
There will also be about 1.5 ounces of fabric on the bottom that will be sewn to the inside of the bag, (where the down would end), loose, (to be able to climb in), with adjustable straps to tighten, (and also doubles as the bottom part of the bivy to retain heat). A GG 1/8" pad will also run from my feet to the top of my seat and will also curve around the sides a little to minimize dead air space.
A separate 1/8" GG pad will also go from the bottom of my seat to top of my torso and will have a slight overlap of the insulation to also keep from loosing dead air space.

The Prequilt alone will be 4.2 ounces.
If I was to add a layer of Climashield I would have another 6 ounces.
I still don't think that would keep me warm enough.

If the down just covered enough to rest under the edges of my body, 4 ounces would give me at least 1 1/3" of loft by its self.
I would like to think that this would be warmer than the .75" from the Climashield.

The total product weight, minus the pads come to 14.6 ounces.

With a little bit of reshaping and cutting corners, it could get down to 14 easily enough.

The whole idea behind this is that it incorporates a bivy into the system. Having this system with a super-lite Cuben tarp and you have a very light bag-tarp-bivy combo.

Aaron,
What do you think the pre-quilted 1.8oz Primaloft One will weight per sq yard? The pre-quilting adds some extra weight. It will be more than 1.8 oz. per sq yard.

I am trying to come up with your numbers on weight but can't.

O.K.,
I changed it, but still have the same finish result.
I had no idea the Prequilt was more than 1.8 ounces.

I have,
Fabric: 6.5 oz
Prequilt: 4.2 oz (3060 square inches = 2.36 yrds X 1.8)
Down: 4 oz

According to AYCE at Thru-hiker.com, the prequilted 1.8 oz basis weight Primaloft P1 is 2.2 oz per sq yd with the scrim attached.

The weight just keeps adding up.

Another ounce for the Prequilt, and I will want the down loft to be 1 1/2", but were still looking at under a pound for the combo.

Thanks for the info.
I'll be making this soon.