Bivvy Bag Problem

[SJStuart]

I spent last night out in the woods hammocking, with my sleeping bag inside a bivvy bag. Woke up this morning, and the sleeping bag is soaking wet on the outside (dry on the inside) while the bivvy bag is soaking wet on the inside (and dry on the outside).

It would appear that the bivvy bag isn't breathable, as it has allowed a massive amount of condensation to build up.

The bivvy bag in question is a Mil-Tec one, with a zipper on the right-hand side.

There was no condensation under my tarp, nor under the cover above me on the hammock (it's the Warbonnet with the "solid" top on), nor on my wool blanket. Basically, everything else was perfectly dry but for the outside of my sleeping bag (which still hasn't dried) and the inside of my bivvy bag.

Is it normal for bivvy bags to collect enough condensation to saturate a sleeping bag? Surely Goretex is designed specifically to allow air through and keep water out... so to my mind if it were genuinely Goretex, this wouldn't have happened, right?

First experience with a bivvy bag... not at all pleased! Any input welcomed.

 

[ozzy1977]

Simon which bag do you have, the one you linked to on the bushcraft store looks very much like the US modular one that I have, I have not used it in the hammock though but had no problems at all on the ground. Your link says Mil-Tec but goes to busccraft store..

 

[SJStuart]

Simon which bag do you have, the one you linked to on the bushcraft store looks very much like the US modular one that I have, I have not used it in the hammock though but had no problems at all on the ground. Your link says Mil-Tec but goes to busccraft store..

I linked to the Bushcraft Store because that's the exact item I bought from the exact place I bought it. It is a Mil-Tec as it says so on the Bivvy Bag's label. Figured I'd link to the exact item I bought so that if anyone else had a negative experience with the bags being sold specifically by the Bushcraft Store, they might be able to shed some light.

 

[Teepee]

All single skin shelters suffer from condensation, even materials with a much higher breathability than the best waterproof/breathable membranes will get condensation in some environments.

The membrane will allow a certain amount of moisture to pass through.. Sleeping in a hammock reduces the breathability as airflow is reduced and less moisture is able to evaporate from the outer surface of the gore-tex. Add to that the much colder temperature that your bivi bag is compared to the inside of the sleeping bag. No matter how breathable a material is, water condenses on cold surfaces and goretex is no different. Gore-tex relies on a temperature differential to tranfer the moisture through the membrane and without that, it won't breath well at all.

My Army gore-tex bivi bag suffers with it. My PU coated nylon bivi is worse still. It's a common phenomenon.

 

[SJStuart]

All single skin shelters suffer from condensation, even materials with a much higher breathability than the best waterproof/breathable membranes will get condensation in some environments.

The membrane will allow a certain amount of moisture to pass through.. Sleeping in a hammock reduces the breathability as airflow is reduced and less moisture is able to evaporate from the outer surface of the gore-tex. Add to that the much colder temperature that your bivi bag is compared to the inside of the sleeping bag. No matter how breathable a material is, water condenses on cold surfaces and goretex is no different. Gore-tex relies on a temperature differential to tranfer the moisture through the membrane and without that, it won't breath well at all.

My Army gore-tex bivi bag suffers with it. My PU coated nylon bivi is worse still. It's a common phenomenon.

So... my best bet is simply to not use the bivvy bag at all?

 

[ex-member BareThrills]

So... my best bet is simply to not use the bivvy bag at all?

that would be my call if hammocking. It serves no useful purpose

 

[widu13]

I would say it's quite uncommon to use a bivi bag in a hammock. As stated it will reduce the bags ability to breathe. You didn't cover your face in the night did you?

 

[SJStuart]

I'm just trying to understand why there'd be condensation only between the bivvy and the sleeping bag, rather than on the hammock cover above me, or the tarp above that. I can understand how there'd be a case for condensation if I were sleeping inside the bivvy bag under garbage bag with no airflow, but under an open-pitched tarp inside a covered hammock with more than ample airflow (enough to feel cold air blowing on my face, which made me opt to throw the bivvy bag in there in the first place) I would've thought that condensation wouldn't have been an issue.
Also, surely then I'd get condensation between the hammock and my sleeping bag when not using a bivvy bag... but that has never happened to me ever (in fact, this is the first time ever that I've suffered any condensation in my setups)

The bivvy bag was used basically to give me the option to pull it up over my head to keep the cold air off me (as I say, my pitch was open on three sides as this was a night to test out new gear and I wanted to expose my setup to more of the colder air than I ordinarily would)

 

[SJStuart]

I would say it's quite uncommon to use a bivi bag in a hammock. As stated it will reduce the bags ability to breathe. You didn't cover your face in the night did you?

For about 10-20 minutes until I reverted back to my wool blanket on the structural ridgeline technique, yes. Surely there wasn't enough moisture in 20 minutes of my breathing to saturate a 6'2" long sleeping bag and 6'5" long bivvy bag?

 

[widu13]

You'd be surprised bud.

Sent from my Nexus 4 using Tapatalk

 

[SJStuart]

You'd be surprised bud.

Sent from my Nexus 4 using Tapatalk

Methinks this warrants further testing... but I hadn't given much thought to my closing the bag up for such a short time while breathing. I'd be amazed if that were enough to produce such a vast amount of moisture, though. My bag is still wet despite spending the whole day locked in a room with a 4KW gas heater and a dehumidifier!

 

[ex-member BareThrills]

i would say its almost certainly your body heat that was driving the condensation. exhaled air has a relative humidity of 100% too so 20 mins breathing in the bag will generate a fair amount of liquid

 

[Dave-the-rave]

Your condensation was almost certainly caused by the fact you didn't need it to stay warm or dry. You were over dressed if you know what I mean.

Edit: That said Mil tec make some pretty crap kit.

 

[ozzy1977]

It is a copy of thr us modular gortex one at a rather high price from what I have found out.

 

[brambles]

I'm just trying to understand why there'd be condensation only between the bivvy and the sleeping bag, rather than on the hammock cover above me, or the tarp above that.

It may be because there was no temperature gradient between the outer of your sleeping bag and the outer of the bivvy bag. Moisture will pass through the insulation and outer of the sleeping bag but then need a further gradient to push it through the bivvy membrane. If you are snugly wrapped in a hammock outside the bivvy there may be no such gradient - the air temp between the sleeping bag outer and bivvy and hammock is going to be pretty neutral as the insulation of the bag is preventing heat loss. The moisture is most likely to be from body perspiration rather than breathing I think. Breath is going to disperse out with the hammock fairly quickly as I doubt it was so severely cold that your breath was rising straight into the tarp, so little chance of condensation collecting there.

 

[SJStuart]

Edit: That said Mil tec make some pretty crap kit.

Yes... if I'd known it was Mil tec, I wouldn't have bought it! Going to contact The Bushcraft Store on Monday and see if I can return it!

 

[BillyBlade]

One of the worst presents I ever recieved was a mil tec M65 copy. It might be a third of the price of an Alpha. But its not even a quarter of the quality.

 

[boatman]

I have never noticed condensation as a problem in my TrekMate bivvy bag. I do sleep with head almost in the open though wearing a woolly hat or balaclava arrangement of a multiple use headscarf.

 

[Hypnagog]

I have the same Bivvy bag and I get a problem with condensation at the foot and under my shoulders.

I never sleep with my face in the bag due to wearing a CPAP mask when I sleep, so all my exhaled air definitely goes outside.

I just presumed it was a bivvy thing and that all bags would do it.

I'd be interested to see how you get on and if switching to a different bivvy would help.

 

[ex-member BareThrills]

I just switched to an e-vent bivvy and so far no condensation at all.