Condensation problems in Vapr Bivy. Suggestions?

[Roger Caffin]

As soon as you impede the diffusion of water vapor with a cold surface, you will get condensation. In general, this means a bivy bag will cause condensation. So why use one? Group think.

I sleep on a Therm-a-rest mattress with a sleeping bag arranged over me as a quilt. The hood goes over my head. The Therm-a-rest surface stays warm enough that there is no condensation. The sleeping bag breathes happily and the outer surface stays above freezing. The hoar frost condenses on the inside of the tent I use. But it is far enough away that it stays frozen. I scrape it off in the morning (with some care!) and throw it out the door. This works fine for a week at a time.

I find it does help sometimes to throw my bag over the tent in the late evening sun (if there is any!): the small amount of heat from the sun plus the very dry air helps dry the bag.

[Anonymous]

Roger, what night time air temperatures are you camping in? Would this happen with even colder temperatures as many of the Forum participants experience in the western mountains of the USA and Canada, especially during winter? Or, would the outer region of a bag’s insulation be the point at which the water would condense and freeze? In this case, could a bivy help to raise the temperature of the outer region of the bag sufficiently to prevent this condensation and freezing within the bag as Vick Hines suggests? You also mentioned tent as opposed to tarp. What differences might this account for? Even the highly educated, resourceful Ryan Jordan finds a use for a bivy – is it only when he uses a quilt and not a sleeping bag? Are the bivy’s functions only related to alleviating wind (quilt use) and rain issues (quilt and bag use)?

[Jeffery Price]

In the specific case that precipitated my first post, I was not breathing inside the bivy. In other cases where this has been a problem for me, I have indeed been breathing in the bivy (with bug net and elevated hood). However, this specific case was the worst I’ve experienced. By “worst” I mean most uncomfortable (because it was the coldest), though there may have been more moisture other times.

Regards,
Jeff

[David Olsen]

If you do without a bivy, the condensation often then forms in the sleeping bag itself, which can be
a bit harder to dry. You will notice frosty hard patches, usually near the face opening and especially anyplace you have dried out wet gear (socks etc.)

In cold conditions, I don’t skimp on insulation underneath me and always use a full length pad
to keep my bag out of any moisture that collects
from whatever source inside the bivy
or tent. Even a 1/4″ of closed cell foam can make
all the difference if your tent is forming puddles
in the low spots from a big downpour.

I use my bivy to contain extra
gear – boot shells, skins, etc. that I don’t want full
of snow- so I put these along side of me to keep
my bag away from the edges of the waterproof bottom and to keep me centered on my pad.

Again the bell is rung for VBL’s if you are traveling
in cold weather for several days.

A hot water bottle
will force out more moisture too and is very luxurious.

I don’t always carry a bivy, but if you anticipate
bugs, high winds, or spindrift, a bivy is one of the
lightest ways to deal well with these problems.
I have tried using just a quilt with a tarp on sub
zero trips and found I couldn’t keep the gaps
closed well enough- though it seems to work fine
in warmer weather.

I vividly remember camping one November at Hart
Mountain Antelope Refuge in Oregon. Temps above freezing and winds about 70 mph. Tried to sleep under the stars in -20F rated polarguard bags. The wind just blew thru and even wearing our parkas wasn’t enough. Just crawling into a wind proof bivy
and suddenly we were warm. We were able to sleep with our bags unzipped and us half out. I have had
similar, but not as dramatic, experiances in Joshua
Tree in the winter.

[S. Garen Szablewski]

This may have already been addressed but if you put your sleeping pad inside your bivy bag you will find less condensation forming under most conditions.

[Author]

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