a different kind of VBL?

R value is around 1.13 times the clo. To clarify, 1clo=1.13R (US if I remember correctly, but maybe SI?). so

As for the VBL idea, it should work. However you would be limited to to only wearing baselayers and you couldn't supplement with insulating clothes easily, such as wearing your down jacket inside the bag. This is a limitation of all VBL bags though compared to VBL clothing.

It would be cheap, and effective, but a VBL clothing and extra down is probably more effective for the weight.

"R value is around 1.13 times the clo."

Yes, I think that's right.

"To clarify, 1clo=1.13R"

No. R = 1.136 * clo

or: clo = 0.88 * R

"(US if I remember correctly, but maybe SI?)."

Yes, U.S. (aka IP).

Hi Dustin and Todd, thank you for the replies. I'm just curious, what is the more weight efficient insulator, down or foam?

I found a place that i can order 24 inch wide EVA foam as thin as 1/16, as well as 1/8, and much thicker (not that i would for this purpose). Here's the site in case anyone one is interested:

http://www.northshoreinc.com/store/pc/viewCategories.asp?idCategory=26

Here's the thing though, down is very expensive, and a new down quilt or bag at this point is way out of the question. This is the extent of my down sleeping gear: 1 EE Rev X 40 degree quilt which i can quickly and easily attach a layer of Apex too, one 30 or 32 degree quilt made by Javan, and one of the older Exped Dream walker Duo quilts that is about a 45 degree.

Then i have a strange quilt i made myself which has a layer of 2.5 oz Apex, then a mix of Angora Rabbit fur loose fiber mixed with 550 Goose Down. While it's very warm (however, no idea what the rating is), it's also heavy at about 2.5 lbs.

If i'm using a lightweight VBL, i don't have to worry as much about condensation, so theoretically i could mix the EE quilt and the one made by J.D. to get a fairly warm system without spending anymore big bucks, at a slight weight penalty because of the extra fabric.

But, foam's pretty cheap, and i could kill two birds with one stone with it, as far as VBL and insulation. I just don't know the efficiency of high quality foam compared to down per weight. Volume is less an issue.

Why not try insultex? Available here: http://diygearsupply.com/product/insultex/

Description from the site:

Insultex Thermal Insulation. 60″ wide.

Insultex is a new, cutting-edge, ultra-light insulation with a wide range of applications. Insultex is an extremely thin, micro-perforated closed-cell foam with a poly scrim quilted both sides. It is easily sewn, incredibly lightweight, very easy to work with, is boyant and retains amazing heat.

Note: While Insultex is technically breathable due to the micro-perforations, it is practically a vapor barrier. This means it is great for underquilts, but for top quilts, you will need to keep vapor barrier considerations in mind.

Sold by the linear Yard.

($6.35)

You'd be able to sew up an insulating vbl

Hi Andy, thanks, that's definitely worth considering. Some initial thoughts: If there is any kind of breathability, i don't think it would work as a true VBL as it would still allow "some" moisture to build up into the quilt or bag which would be a problem for extremely cold temps.

I suppose i could throw one of those SOL PE reflective blankets over the top.

I've heard that this stuff has major durability issues though, which would be my other main concern besides some moisture passing through. EVA foam on the other hand is very durable for it's weight and thickness.

Whoa! I just had an Arctic concept epiphany.

Sew up a "bag" using the Insulex material. Take 2 layers of 1/16th foam and make it wide enough to drape over yourself fully.

Then start cutting out parts of the foam in criss cross (basically you will cut out squares at different points). So you have two holy foam layers, but with some structure.

You get inside the Insulex "bag", lay one layer of the foam on top of you, then lay a reflective blanket on top of that layer.

Then you layer the other foam layer on top of that, and then your down jacket, then large Down quilt goes over the top of all that.

You get a tiny bit of breathability/moisture venting from the sides, but no moisture in the down quilt or jacket. You also get some of the IR reflected warmth back because you have some air space on both sides of it.