suitable use for a cuben bivy

The cuben bivy is only cuben on the floor. The top of the bivy is the same water resistant breathable argon or m90 or whatever he is using these days on all of his bivys. If the entire thing was made of cuben condensation would be unbearable just as you fear.

His snowyside bivy sounds like it might be what you are looking for, but it is much heavier.

I have slept in a Borah Gear sil bivy w/a M90 top on snow. Lows were around 20 degrees. Lots of condensation inside the bivy. My down bag has a good performance shell, so no biggie, but I was surprised with the amount of condensation. I think it is just a bivy thing.

I made an Impetus 1.1 bivy and have had very good luck with it.

Enough that I now use it all the time. It helps with punctures, keeps everything clean and keeps out the drafts a little better with the quilt..
The Impetus has a different feel and does not cling or settle on to the bivy fabric.
This keeps a bit of air between the layers which helps a lot with the condensation.

I've made an M90 and M50 bivy and both have considerably more condensation.
I wish the Impetus 1.1 would come back in stock soon.

ahh- that makes sense, I see the top is "Argon"- my looking around shows there are a couple of versions (maybe more?), different breathability, different HH's- I have an email into John to see which he uses

I think for snow caves/trenches a little more HH might be worth a little less breathability????

Cutting up to make into stuff sacks.

^ :) after more reading, looks like eVENT (w/ cuben bottom) is what is called for, of course it triples the weight (4.5 vs 13.5)

unless someone has a different idea for a top?

thanks

That is the age old question. What kind of protective material can we use in bivys that mitigates condensation and keeps the bivy in the sub 6 oz range. My solution is a tent in winter and bug bivy with bathtub floor the rest of the seasons.

Currently condensation is just part of using a bivy, especially in the winter. I'm hoping technology changes that soon.

My cuben drybag for my sleeping bag literally wore out, near the top where I held on to it when stuffing the bag. I just threw it out yesterday in favor of a slightly heavier "ultralight drybag".

I'm no expert on cuben, but there are different thicknesses at least, so factor that in when I say …

The cuben upper to my tent has lasted what I guesstimate at 500 nights of use or so. My cuben pack cover and cuben rain skirt are both going strong; less actual use, but a lot of being carried around in the external mesh of my pack. Anyway, I'm not anti-cuben (!).

But areas where significant wear occur in just daily use suggest to me a limited lifetime for cuben fabric. I would suspect that could be the case for a cuben-lower part of a bivy.