down bag, bivy & condensation

[Headshed]

I have an old Karrimore foxhole hooped bivvy, that would fill up with condensation without fail. Then I realised that if I keep the zip open partially (say 2~6 inches) or only leave the mesh closed then the problem went away. Not had a significant problem since, although I do also air the sleeping bag to allow moisture out between uses. Good article!

 

[petrochemicals]

The Book of THE BIVVY says on page 49:-

For moisture to pass across the breathable membrane of the bivvybag it needs to be:

• warmer on the inside than the outside;
• more humid on the inside than the\outside;
• have a breeze across the surface.

if none of these is the case, then you might as well be lying inside that impermeable orange plastic.

its a good book and is worth a read, but basically you do need some air flow across the bag. to quote the author:-

THE WARMER THE WETTER.

Or to put it more bluntly:

SHIVER- OR DRIP

Hope this helps

blimy this thread cummup again,

I'll add to the quote wet , heavy dew, rain, frost . The bivvy can only be used as a wind break, rain guard, which asks questions of alot of bivvys. The solution is hooped bivvys with real vents. I would say if your using one under a tarp a straight pertex bivvy would suffice as a sleeping bag cover for most as its very highly breathable, I don't know how it would act under rain conditions though. Not sure about pertex shield, far less breathable.

Thats a really bad bivvy book,