Tackling bivi condensation

[Paul_Davies]

So it seems no matter what bivy you use you're always going to be prone to the dreaded condensation issue.
I'm using a hooped bivi and found it to get pretty wet between the bivy fabric and the top of my down quilt.
I'm considering trying adding a large microfibre towel as a sort of blanket on top of my quilt.
Was wondering if anyone has tried this have experience or have any advice on this?
I figure yes the condensation volume won't necessarily be minimised but maybe the microfibre 'blanket' would absorb the bulk of it reducing the condensation pooling or beading in the bivy?
Cheers, Paul.

 

[MrEd]

I have bivi slept a lot, from envelope bivis, to single hoops to my terra move double hoop and ventilation is the key.

In the double hoop that’s easy as it has vents too and bottom, but in the envelope or single hoop less so.

In the envelope style I used to just sleep with my face exposed, and with the single hoop I would have the vent open (ditch army bivi) and would wear a hat etc.
I was sure almost all of the condensation was from my breath rather than body heat. I found it would have condensation in the upper quarter round my head nothing in the middle and then condensation round my feet (presumably as that’s the least ventable area)

Do you sleep completely zipped in with your face inside?

A blanket may well absorb some of the condensation and worth a try.

 

[Paul_Davies]

Yeah ive gone ahead and purchased a large microfibre towel and ill give it a ago as an extra condensation layer.
I using a alpkit elan hooped bivi so no foot box vents and I always sleep with the head vent open.
Generally its condensation free but on those dewy starry nights especially now in autumn I have experienced a wet bag. Body heat and weather I imagine.

 

[Danceswithhelicopters]

What fabric is the Elan?

I've found that anything other than Gore tex doesn't breathe enough for me. Also, I've found my sleep setup to make a big difference. Properly changed for bed so damp day clothes off, merino top and/or bottoms depending on the weather, sleep pad outside bag so plenty of space in the bivibag for air and definitely head out with a hat as required.

 

[Ozmundo]

I’ve only had condensation in bivies and micro tents that enclose the face. I just don’t use them now and go with the sleeping bag cover style and a small tarp for the upper body.
The micro fibre fabric may work, be interesting to know. I often have quite a large micro fibre towel rolled up as part of my pillow (I swim a lot).

 

[Pattree]

I know I’ve said this before on BcUK but here goes:
I have never suffered serious condensation in my bivi sack.

I’d never use one of these modern sausage skins. I use a large size 90pattern system or the 90 bivi with a Snugpack Chrysalis 5. (Snugpack’s big mistake but there you go). I’m big but I can get dressed and undressed inside this bivi and that’s with a three quarter sleeping mat INSIDE the bag. Did I say, it’s big?

I use it upside down so that the hood comes loosely over my head. I’m a winter camper so that said head is snug inside the sleeping bag. The hood is huge and my boots keep it in place in windy weather.

If you can get hold of one then you will probably need to re-waterproof the seams. The seam seal tape gives up after thirty years or so. I just paint them with Fabsil once a year.

 

[Ozmundo]

Upside down. This is the way.

 

[Pattree]

Only if you normally sleep standing up!

 

[Barney Rubble]

So it seems no matter what bivy you use you're always going to be prone to the dreaded condensation issue.
I'm using a hooped bivi and found it to get pretty wet between the bivy fabric and the top of my down quilt.
I'm considering trying adding a large microfibre towel as a sort of blanket on top of my quilt.
Was wondering if anyone has tried this have experience or have any advice on this?
I figure yes the condensation volume won't necessarily be minimised but maybe the microfibre 'blanket' would absorb the bulk of it reducing the condensation pooling or beading in the bivy?
Cheers, Paul.

I'd be curious to note whether you've encountered condensation when using a gore-tex bivi bag?

In my experience fabric is absolutely vital on a bivi bag and gore-tex has been the only fabric that has worked well for me in terms of breathability. I've spent dozens of nights in my British Army gore-tex and Dutch army hooped goretex bivi's in all seasons for many years without any problems. Admittedly, I always leave an opening in the head end (even when it's raining)! But in all honesty, even with good ventilation, the sil-nylon type fabrics that you find on the lightweight bivi's such as the Alpkit, Snugpak (and other) bivi's don't seem to cut the mustard.

 

[Chris]

I never had condensation issues in the old issue Goretex bivvy bag - this was the plain olive green one. Cracking bit of kit, I regret that I didn't 'lose' that before I had to give it back. You can get them for a fairly reasonable price these days though, though I think the majority will be MTP now.

The new Snugpak Special Forces bivvy bag I have I haven't had to use in anger yet, but I suspect it may be prone to condensation.

 

[Ozmundo]

I have the British Army one and previously a Mountain Equipment one of similar large size. It was a bit lighter and had a zipper accross the head/face but otherwise feature less.
Both Goretex and I’ve never had condensation in them using the issue or snugpack sleeping bags.
All weathers in the Welsh mountains.

The hooped bivies I have tried, one was the Dutch (Fesca?) and a French or Canadian thing. The later was a self contained bath, kip mat was floating….

 

[ged]

I have two British Army Goretex bags - the old style laced laced ones. Nothing comes close in my experience.

If I use a tent - rare thesedays - I still use a bag, just so that the condensation inside the tent doesn't soak into my sleeping bag.

Once upon a time I went to sleep in a dry hollow and woke up with the bag lying in half an inch of water. Dry as a bone inside the bag. I have looked after it well though.

Another time after an exhausting tab in a memorable storm I took off my boots, got in the bag fully clothed and soaking wet, passed out, and woke up next day snug and warm and dry. I'm sure the bag saved my life then.

There are things they call bivvies which resemble small tents made of fabrics which are impermeable to water.
I don't call them bivvies. As others here have said, most of them are more like a cold Turkish bath.

 

[MikeLA]

Never had condensation my issue bivi bag. Slept in all weathers

 

[Falstaff]

I have the Alpkit Elan and don't really have a problem, but as said ventilation is the key. If there is no air gap between body and bivi then it cannot ventilate and will wet out
1) fashion a stick to raise up a guy line at the foot, and create a tension line "ridge"along the bag to the head - holds it off the body
2) shove something substantial down the bottom to also hold the foot open at the sides - ration box, bike helmet, boots in a plastic bag etc. ( stops the boots from freezing too).
3) leave the head end open and the head outside the covered bag area to breath, woolly hat if getting cold, get the head end mesh "window" vent open too- I find it can condense a bit if the main fly screen is fully closed and often leave a gap in the zip if the critters aren't bad.
4) Consider putting a mini-tarp over the top end - stops rain and seems to help with heat/condensation. I tie the tarp foot to the frame and peg it at the bottom or tie a ridge line from the frame to the foot and pole it out with a couple of sticks etc.

 

[Falstaff]

Mr Ed mentioned the sleep mat being outside the bag. If it's a thicker pad then definitely outside as can reduce internal volume/air a lot. I use a skinny pad or foam roll no more than 12mm, so get away with it being inside and clean.
I've not thought to try my thicker 20mm Thermarest with the bivvy but think it needs to be outside. I also have two DIY groundsheet type bag/mat protectors I always use - one is a piece of breathable fabric roofing membrane, weighs/bulk nothing, t'other is a chunk of cut down HD tarp, a little bit bulkier but not much or heavy, and bombproof against all but thorns.

 

[MrEd]

Mr Ed mentioned the sleep mat being outside the bag. If it's a thicker pad then definitely outside as can reduce internal volume/air a lot. I use a skinny pad or foam roll no more than 12mm, so get away with it being inside and clean.
I've not thought to try my thicker 20mm Thermarest with the bivvy but think it needs to be outside. I also have two DIY groundsheet type bag/mat protectors I always use - one is a piece of breathable fabric roofing membrane, weighs/bulk nothing, t'other is a chunk of cut down HD tarp, a little bit bulkier but not much or heavy, and bombproof against all but thorns.

I have a 20mm thermarest and while it can fit inside I don’t like it, and I too use mine on a ground tarp - I use a small footprint from an old one person tent that got binned years ago

 

[tamoko]

No one bivy have enough ventilation, so condensation are guaranteed like in your footwear in winter.
Only wapor layer works to keep isolation but you will be swim inside, but warm. Same for Shoes.

 

[Pattree]

Condensation comes from two main sources:
1. Any wet clothing etc that you bring into your bivi.
2. Your breath - this is by far the biggest contributor to condensation as it cools from body heat to ambient (outside temperature.). One person can breathe out up to 350ml of liquid water overnight.
(3) Sweat is mostly absorbed by your clothing or your sleeping bag liner.

Partial Remedy:
By leaving your face uncovered or loosely covered you will eliminate most of the potential condensation. Your breath goes straight outside.

I’ve already said that my way if doing this in a 90 pattern bivi is to use it upside down with the hood loosely over my head if it’s going to rain. It is the sleeping bag hood not the bivi that keeps my head warm in winter.

If you are determined to shut yourself into an oversized condom or a canvas coffin then you are bound for maximum condensation and quite possibly a headache as you run low on oxygen.

 

[DocG]

I like to be under a wee basha - even a DD Magic (Flying?) Carpet type rather than nothing - inside a bivi bag. I also like a small ground sheet under me + a 3/4 length mat (sawn-off issue type). Hiking poles = o/n basha poles with a couple of titanium pegs and some paracord. Basha and sheet add a little weight but more than make up for it in comfort, IMHO. They also improve admin space.
+1 for older issue goretex bag.
With above combo I have chased / assessed DofE groups all over the highlands and enjoyed the experience for most of the time. Condensation has never been an issue, although I have slept on top of my bivi bag in warmer weather.