Bivy bags and condensation...

[Polisherman]

Now I'm not the most experienced bivy bag user, and seeing as the BB200 is not far off I went out this weekend for a little sleepover.
Conditions were perfect, clear, light breeze. I followed the Pennine Bridleway south from Saddleworth to Roych Clough, and at about 10.00ish I found a flat bit of grass just behind a wall.
Now I do know from experience that sleeping in damp clothes makes for a chilly night, so quick swap into a set of Helly's and snuggle in.
I did expect some condensation of course, and I felt dry in my down bag apart from when the Rab Storm "lid" kept flopping in my face. In the morning when I pulled the bag out of the bivy sac everything was soaking. No big deal 'cos I'm only out for a night, but how do you deal with multi-day trips without waiting around airing things?

[JohnClimber]

Never had a problem like that in my Borah bivi bag but it does have a large midge nettting area to help it breath.
Could you have had it closed around your face too much?

[gentjim]

How soaking..? I have a lovely TiGoat bivy, which I was actually a bit worried about for a while, as I could see moisture against the upper shell in the morning sometimes. But then I realised it was only in certain conditions (when warm and sheltered), and that despite my *terror* of any damp on my down, the bag dried in seconds as the dew-point was simply between my bag and the bivy, leaving a sort of surface layer which dried out quick.

I'm actually in the middle of reading the brilliant "Book of the Bivy" which is much more fun and less geeky than expected and his view (over-simplified) is that you can be warm or dry, but not necessarily both. By which he definitely doesn't mean you should be soaking, far from it, but basically says that if you're on a breezy hilltop, you have good conditions for dryness (moving air, and a temperature gradient between inside the bag and out), but if you're sheltered and warm, you should try to vent the bag as much as possible, as moisture will build up without those 2 things.

Hope that helps a bit. Recommend the book - there's a kindle version (for asking along on your phone to the hill), and he's updated the 2015 edition.

[Bearbonesnorm]

If conditions are 'right' then a certain amount of condensation is pretty much inevitable, although you can reduce it thus;

1/ Don't enclose your head inside the bivvy.
2/ Don't wear damp clothes or put anything wet inside the bag.
3/ Avoid getting too warm during the night.
4/ Use a tarp or find some kind of over-head cover such as low trees, etc.
5/ If the ground is wet use a waterproof groundsheet below the bivvy bag.
6/ Aim to pitch where there's a breeze.
7/ Avoid pitching next to still water such as lakes.
8/ Avoid pitching on valley bottoms, especially if there's water there.
9/ Use a bivvy bag with a breathable base as well as upper (such as a Hunka).
10/ If you do have a fully breathable bag (ie top and bottom, see above) place your mat on the outside of it.

There's a few more ideas that help but I'll save those for the book

[Polisherman]

OK, looking back on it I failed on...

Points 1&2!

I stopped riding and within 15 mins I was in my bag. It was a BIG mistake to put my sweaty t-shirt and shorts inside the bivy bag. Then I put the bag over my head "just for 10 mins to warm up". Before I knew it the top flap of the bag was wet and flapping in my face!

Live and learn eh! ;-)

[whitestone]

I tend only to fully enclose myself in a bivvy bag when the flying death are about . Certainly in summer, Stu's point #6 is worth considering for that alone Really the bivvy bag is there to stop any such breeze from constantly removing heat from you. I find that even though my bivvy bag has a hood I'm better off with my head and possibly shoulders outside it. If the wind's that strong then I can put sacks, etc on the windward side and just have the top part of the bag sheltering me on that side only.