Just when I thought it was safe

[Moondog55]

Seems Cecile and I cannot help ourselves where a fabric bargain is concerned. We have just met the old designer for Rip Curl ski suits [ The Alps 3000 series] and have come home with most of a roll of 85GSM Thinsulate
Naturally I have lost all the data that 3-M sent me
But because this is scrimmed on both sides it should be very easy to work with and I'm wondering about another sleeping bag overbag and not getting the OP Cocoon.
So the question is has anybody ever heard about the use of the scrimmed insulation without any shell fabric?
I'd be using the Goretex bivvy on the outside so putting a shell fabric on the outside seems a little redundant
So how warm would a couple or three layers of this be>?
Herself has already sold on a few metres to people in her sewing group to make chiller bags with

[Moondog55]

Found the data sheet
This must be the 74GSM stuff not counting the double scrim layer
http://multimedia.3m.com/mws/media/7453 ... eyline.pdf
So a double layer is about 2.5Clo

[Moondog55]

So it was a quiet day here and I used a couple of hours to cut some fabric. Cecile has sold some to members of her sewing forum already, she has asked and is getting $5- a metre. We are recommending a single layer for sleeves and hood and a double layer on the body for casual warm wear
I used 4 metres for this quick overbag which still needs the wedge in the centre front.
I also now realise why all the Chouinard gear for climbing bivvys was the shape and size it was, They simply cut the bivvy sleeping bags to use the full 60 inch width of this scrimmed insulation Duh!

Attachments

Foot end
Sized to fit my Ultra

IMG_0227.JPG (104.5 KiB) Viewed 14521 times

Simply gathered at the batting edges

IMG_0228.JPG (107.46 KiB) Viewed 14521 times

The Ultra is a bit wider at the top than the batting is wide Wedge to follow

IMG_0229.JPG (112.21 KiB) Viewed 14521 times

[Moondog55]

No point in using the overlocker on this, I'll just hand sew it.
I just weighed it
600 grams
No point in adding a shell; if I use it the insulation will always be between the sleeping bag and the bivvy sack.
600 grams of down would naturally be a lot warmer but then there would not be the moisture barrier effect of the synthetic layer

Attachments

The wedge added and I managed to get a full 3 layers of insulation over the torso

IMG_0230.JPG (102.1 KiB) Viewed 14513 times

IMG_0231.JPG (106.59 KiB) Viewed 14513 times

[CasualNerd]

Is an overbag likely to be warmer than the same amount of insulation in one bag ?

I mean it would be heavier overall, but would the extra layers trap heat better ?

[Moondog55]

There is a lot of debate but there is no doubt that the extra weight in down and shell in a single bag is warmer. What an overbag gives is versatility because a -50C bag is pretty much useless for most of us most of the time and getting an overbag may be the cheapest solution if you already own a good down bag
The other point that cold country sleepers make is that any moisture gets pushed out of the down and into the synthetic over layer keeping the down dry
Personally I believe that the air-gap between layers adds to the warmth of a double bag but I have seen no scientific reports that validate this belief although it has been proven in clothing.

[rcaffin]

The other point that cold country sleepers make is that any moisture gets pushed out of the down and into the synthetic over layer keeping the down dry.

That has been our experience too. (Except that it was a down over-bag, but no matter. The inner bags stayed dry.)

Cheers
Roger