down bag, bivy & condensation

[gazza300]

Hi y'all

so last night (late August) I had my first night in a new bivy and down bag combo - Rab Survival Zone and a Cumulus Ultralight 200 bag. I have a Vango ultralight inflatable mat, which was outside of the bag. I did a bunch of research about bivvies and sleeping bags and ended up with the best that I could get (in terms of what I could afford). Trial run in the garden as a test.

Anyway, I woke up several times, not actually cold, but not actually warm either. I was toasty when I went to sleep. My bag is rated 3 degrees comfort zone, it was around 17 degrees last night down here in Devon. Sky sometimes clear, sometimes a bit clouded. It was apparently high humidity ~80%.

As well as waking a bit cold, when I got up this morning the inside of my bivy was wet. My sleeping bag has DWR and it coped, but was damp on the outside. I didn't have the bivy closed up at all, although I guess I may have slipped down into it in the night, but each time I woke my head was outside. Very disappointed, I had high hopes of lightweight, stealth camping.

So my question is, would high external humidity cause extra condensation in my bivy? Would the condensation be responsible for cooling me down? Is my sleeping bag or bivy bag crap?


cheers

 

[Shewie]

You can get condensation at odd times when out, sometimes it just needs to be still with no wind and you can get it. A warm body inside a sleeping bag can create enough of a difference to the outside temperature that condensation will form then too.

In a nut shell, no matter what kit you have sometimes you'll get condensation. The best thing to do is take the sleeping bag out of the bivvy and just let it air out for half an hour. You could go out again tonight in identical conditions and not get any.

 

[Clouston98]

Yeah it's just one of those things that happens sometimes but not others.

I have a rab ridge raider, nanok airlock -5 and a mountain equipment Helios mat and have had condensation before but not very often. I would probably say it was down to the humidity but you should try again another cooler night and see how it goes.

 

[gazza300]

Thanks for the replies guys.

I'm going back out there (all the way to the bottom of the garden) to try again tonight.

I'll post an update tomorrow, just for completeness.

 

[Clouston98]

Good look!

 

[spader]

Some photos of the setup would be great. cheers.

 

[mousey]

I ended up just sleeping competley outside of my bivvy bag, although when it looked like it would definatley rain I would get into up to my waist - so if it started in the night I could just pull it up over me [I didn't have a down bag while using my bivvy].

Since then I have ditched a bivvy bag in favour of a tarp. Getting in and out of a bivvy bag while it is actually raining [and keeping dry] is a right bugger

 

[Dave-the-rave]

Breathable materials like gortex are a bit funny. I don't remember the science of it but basically if it's warmer outside than inside, the material can work in reverse ie will let moisture in rather than out.

 

[knifefan]

Over the years I have used many different types of bivi bags - some cheap and some very expensive and without fail "ALL" have suffered condensation!! as with all single skin shelters (including tents & tarps) so long as the outside temperature is lower than the internal temperature you will get some condensation!! No big problem, but the best solution is to use a synthetic sleeping bag - which will not suffer as much as a down bag!!

 

[petrochemicals]

x2 definatley for a synthetic bag.

 

[gazza300]

thanks for the replies.

I kipped out again last night, similar conditions, ~ 16 degrees, still, clear then cloudy. I used my silk liner (forgot it last night), it helped with the warmth, I woke up a bit sweaty...

Anyhoo, still had condensation in the bivy when I woke up at 4am, so I thought hey, why am I in here anyway? it ain't gonna rain. So I got my sleeping bag out of the bivy and just used the bivy as a groundsheet. Unsurprisingly, no condensation..

I'm guessing that overall I was maybe too warm in there for the bivy to cope with moisture transport?

I really wanted to have this nailed as I'm going to Bialowieza forest in eastern Poland in a couple of weeks and plan on a mixture of camp site and stealth camping. I guess I'll be taking a smallish tarp along for the ride, keep my options open.

cheers

 

[gazza300]

@mousey I'm thinking along those lines, having the bivvy ready to use. Also going to check a smallish tarp.

 

[Joonsy]

I have also suffered with condensation in bivy bags too despite using them correctly, have used four types all advertised as breathable and waterproof and all suffered, have even suffered when the condensation turned to ice inside the bivy bag on a very cold night. I have found that weather dictates their usefulness, and unfortunately they are at their most useless when you need them most, when it is wet and still and humid they suffer condensation sometimes considerable, when it is dry and breezy you suffer less so. Therefore I have come to the conclusion that they work in reverse, when it is wet and humid and you need them most they don’t work and suffer with condensation, when it is dry they do work but you don’t need one then anyway. It is sometimes said that you can plan in advance and choose the suitable nights for using a bivy, which seems to me to suggest further that they are unreliable as it is not unknown for weather to change and anyway I like to go when it suits myself not my kit. A bivy bag is okay to pack for emergency on an unplanned night out but personally I have found that a tarp is far more useful than a bivy, and I use a small one, however with a tarp some sort of groundsheet is needed for a down bag and sooner than take a groundsheet I do take a bivy bag and use that as the groundsheet instead and just lie on not in the bivy and that way I have all options covered. This being said I have many times travelled with a bivy bag only using various shelter/old barns etc etc and carried a bivy for emergency only not intending to use it but having it just in case, a lightweight way to travel but you have to improvise somewhat as campsite will be dictated not chosen travelling this way which is not always possible in some areas, having a small tarp is a better option and just use the bivy for a groundsheet and optional emergency use.

 

[Clouston98]

It's only a bit of condensation and it doesn't really matter and certainly doesn't make bivvys a no goer in my opinion.

 

[rg598]

In my experience you will get condensation in just about any bivi. None of the waterproof bivis will let sufficient moisture out to prevent condensation in all conditions. High humidity and low temperatures will make the problem worse.

 

[rickyamos]

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

 

[fellwanderer]

You can still use a down bag with a bivvy and staying dry by not closing the bag completely and using the bag in conjunction with a tarp, breathing in the bag will produce lots of moisture

 

[Uilleachan]

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

^^^^^ This

O grade biology and semi permeable membranes, anyone remember those experiments?; the equalization of salts in solution etc. That was the material/technology used in the original gore-tex. The above is the main reason I moved from using gortex for summer hill loch fishing, "summer" being a bit of an oxymoron where I live, but every now and then the temp does creep high enough to make gortex worse than useless, in warm wet conditions.

 

[Andy BB]

Goretex also loses it's "breathableness" in sub-zero temps.

 

[rik_uk3]

Over the years I have used many different types of bivi bags - some cheap and some very expensive and without fail "ALL" have suffered condensation!! as with all single skin shelters (including tents & tarps) so long as the outside temperature is lower than the internal temperature you will get some condensation!! No big problem, but the best solution is to use a synthetic sleeping bag - which will not suffer as much as a down bag!!

Is about right unless weight is a real issue. Better still use a tent and dump the bivi bag/tarp. Not all single skin shelters (including tents) will wet you, it depends upon size and other factors. I really do see the appeal of using a tarp, the romantic notion of them, me Vs wilderness et al but in reality and in my view a bivi is just that, a bivouac and great for emergency use or for a summer day/night trip in the woods; in winter I'd have only used one if it hit the fan and my main shelter failed (just my pennies worth).

For most of the UK I'd say go synthetic if you can carry it.