I was looking at a rather nice down vest on the internet and the description says that, half its weight is the down itself, the other half is material. Although slightly impressed, I thought why don't they make the thing out of Cuben fibre?

It would result in an even lighter garment and it would also be much more weather resistant (although not waterproof due to the seams). I know Cuben doesn't breath but I don't see that's a problem with something like a vest ... unless the inability to breath means that you can't compress the thing, which also means it can't loft. If that's the case then surely the main panels could be Cuben or possibly just the outer shell.

Any thoughts or should I just stop thinking as much ?

What is Cuben fibre? The name rings no bells at all -maybe thats just my dementia!

What is Cuben fibre?

Expensive, very light and very strong It's started to gain quite a following with tarp makers, etc in the States and is just starting to appear more readily over here. It's almost see-through and rustles like a crisp packet in a breeze.

This'll explain it much better than I ever could.

http://www.cubictechnology.com/

You have answered your own question really. It can't breathe so your persperation will consensate inside the outer layer and the down will loose it loft. As you say, if it was inner skin too, it couldn't loft and you would also sweat inside just like any impermeable garment.

I'm not sure it's actually any lighter than the downproof fabrics used for ultralight vests etc, they are around 20-30gsm iirc.

Terra Nova make a cuben bivvy bag: super light, not breathable so an emergency shelter only, and rediuclously expensive.

I've seen the Terra Nova bivvy bag

The silly thin cubens are 19gsm and a lightweight breathable downproof fabric is 26g, so yup it is 'lighter' but the diference would be negligable overall and of course it doesn't sew well so not sure how well the baffles would cope. You would also loose that lovely silky soft feeling you get sliding into a well lofted piece down clothing :D

And if it sounds like a crisp packet it may also be slightly annoying maybe?!

And if it sounds like a crisp packet it may also be slightly annoying maybe?!

No maybe about it ... here's Ians very loud Z Packs tarp in action

Ahhh, it is possible. I've just lifted this from a US company who produce Cuben down quilts.

The Epiphany is a high performance VAPOR BARRIER quilt. It is made of fully waterproof and extremely light CUBEN FIBER. We use no-sew baffling completely eliminating the possibility of body vapor entering the insulation from the inside or precipitation entering from the outside. With the removal of body stitching we have added a stripe of nylon into the foot area of the quilt. This stripe is covered by a CUBEN FIBER inflation tube that is used to fill the quilt with air. This allows the loft of the 850fill power down to be variable.

If it can't go through it, what happens to the 1pt+ of sweat your body produces during the night

It's a vapour barrier quilt, "Vapour Barrier Liner for use inside sleeping bags in very cold conditions: prevents evaporation from entering and icing up inside the down layer."

Or have I missed something? Must be like sleeping in a up market tin foil bivvy bag.

If you're into temperatures requiring a vapour barrier, the chances are your not worrying about the 20g of weight you might save by using Cuben.

Hence for summer bags where every gram counts, the little you save with cuben isn't going to offset the nasty nights sleep your likely to encouter.

here's Ians very loud Z Packs tarp in action

But it's not as loud as Taylor's mate

Interestingly I notice ZPacks are now listing a breathable Cuben at 48.3g/m

I'd like to comment but my z-packs bivy has been lost in customs/ post office no mans land for over a month....grrrrrrrr :evil:

All this talk of Cuben fibre is affecting my mind; when I think about kit I own that I previous thought was about as lightweight I now know there's a lighter option...

...and last night I'm reading about Kurt Refsnider's TD kit list and he makes this comment "I also carried some homemade, compact cuben fiber mitts and oversocks that are truly waterproof". I wish I hadn't read that.

http://salsacycles.com/culture/kurt_ref ... ide_setup/

Cuben fibre Seatbag

Would love to retrofit cuben fiber to my Revelate saddle bag considering it weighs in at nearly 400 grams empty.