I got a bit of extra pay this month so thinking of treating myself to a Borah bivy bag. I've used an AK Hunka in the past but found condensation to be a bit of a problem.

Firstly will I notice a difference in condensation with a borah bivy and does anyone have any idea if there is much noticeable difference between the M50 and M90 fabrics?

Also I've noticed with a silnylon tarp that water tends to condense on it quite readily when the temperature drops. Has anyone notice a problem with this happening on the silnylon base of a borah bivy?

Thanks for any advice,
Mark.

M90 is more breathable than M50 but less waterproof and a touch heavier. I sometimes get a little condensation in the foot end of mine (M50) if the conditions are right.

Never really noticed any on the base.

If I were buying another I'd get an M90 top.

I asked John a few questions before buying mine. He had this to say which might be relevant:

You are correct, I almost always recommend the M90 for use in the UK. It's by far the most breathable, while still having a great DWR treatment.

An example of a popular hood modification is in the attached picture. That modification costs nothing extra, so it is the most popular. It is also the most effective at keeping the breathability while adding more protection.

I got the hood mod (which makes the net section at the head end more of a pillar box slot) because I thought it would be better for UK.

Embarassingly it's still in a gear box as the few trips I've done since ordering it have been hanging.

For a bivi bag (compared to my old Phoenix goretex bag) it's incredibly compact and light weight. So much so I'd be a bit worried about its performance if not for Stu giving it the big thumbs up 8-)

Im waiting for mine to arrive, apparently its on its way :)
I asked John about Breathability v's Waterproofness and he advised M90. I thought breathability more important as its mainly for under a tarp it will have some protection against the rain.
I also got the hood modification
Mart

I went for the M90 and (so far) have had no real condensation issues and am really happy with it's performance.

I loike the sound of this bivvy, when funds allow prob a good upgrade ocer my hunka which I also suffer from condensation with.

Thanks for the replys guys. Think I'm erring towards the M90 for the breathability and I plan to use it under a tarp.

Mark.

Just got hold of mine, in came in a box smaller than I was expecting (a great start). Very impressed with both lightness and quality of workmanship. I got a reduced netting hood, L shaped zip, tie points at the corners on M90 upper fabric. Think this should about cover every option
Communicating with John was great, he patiently answered my questions and advised where appropriate
Allow around a week and a half for the postal service to do its thing

Cant wait to try it out
Mart