Bive sacks

EmsRescueGuy

EmsRescueGuy

Joined
Oct 21, 2006
Messages
1,067
I just got A bivi sac for christmass its nylon supposedly breathable but i awoke with the outside of my sleeping bag (inside the bivi) quite wet while using it camping in a tent last night. I had this same problem when i used a heavy tarp like emergency blanket over a thinner bag once but figured that was due to it being plastic. I know that i tend to sweat alot but i had changed clothes before bed and was not excessiveley sweaty.

Anyway is this normal has it happened to anyone else, Shold i mabey put a few gromets to vent the bag are there any other suggestions?
 
all i can think is that it is due the inside temp being higher than the outside temp when the two meet at a surface(no matter what) you will get condensation of the water in the air so hence happens more on humid days than dry.
 
Ever worn a full face rebreather mask? Fogged up. You exhale several pints of water vapor in your sleep. Where is it going to go? This is why I like a higher (and vented) shelter in winter.
 
I have spent alot of time in tents and bivy sacks over the years and one thing is for certain - without ventilation they will all form condensation. If the Bivy sack has vents in it, open them up. If the door has both a mesh and a solid rain-fly, zip up the solid rain-fly about 3/4 of the way and leave the mesh open for ventilation. The key is to have a good bag and appropriate clothing in order to be warm with the vents open, otherwise all that hot air you expel with condense and soak everything in the sack.
 
Wearing clothing such as cotton in a sleeping bag tends to accentuate moisture accumulation as cotton absorbs moisture readily but doesn't wick very effectively. Try wearing poly long johns (or silk) instead. If your bag is too light, wearing heavy clothing inside won't help much. Make sure it's rated for the temperature conditions you use it in.
 
EmsRescueGuy said:
I just got A bivi sac for christmass its nylon supposedly breathable but i awoke with the outside of my sleeping bag (inside the bivi) quite wet while using it camping in a tent last night. I had this same problem when i used a heavy tarp like emergency blanket over a thinner bag once but figured that was due to it being plastic. I know that i tend to sweat alot but i had changed clothes before bed and was not excessiveley sweaty.

Anyway is this normal has it happened to anyone else, Shold i mabey put a few gromets to vent the bag are there any other suggestions?
Click to expand...

I had an OR bivy sack years ago and I got rid of it before it killed me. It was a Goretex type. Once in the winter I had a pile of snow close up the opening to my bag. Woke up with a real bad headache. I think I was lucky to wake up at all. I believe that I had carbon dioxide posioning. Very unpleasant as was the fear of getting back into that damn thing. I used it once in the summer in a heavy rainstorm and had to batten "down the hatches". The temperature went high enough to melt solder in seconds.

I think they suck and can only think of a very few circumstances where I would consider using one.

The only thing those bivies sacks don't have is the handles. If they had the handles they would be perfect body bags.

KR
 
EmsRescueGuy, What sort of bivy do you have? What were the weather conditions when you used it? Did you have a tarp to sleep under, or were you out in the open? Maybe you need to play with your setup (bag, clothing, vent options) a bit.

I have a GoreTex Outdoor Research bivy that I/we (it's a double) have used without any unfavorable incidents. Even in chilly weather, we've kept the opening by our heads cracked at least 8"-10". It is a double-hoop sack, so maintaining air circulation through the sack is pretty easy. We've really enjoyed our OR GoreTex bivy, and will continue to do so.

I also have a $30 "waterproof-breathable" bivy that is more or less a coated nylon sleeping bag cover with a net that zips over your face. I got it last year from The Sportsman's Guide just to try out. I've only used this one on one trip. The overnight temps on the trip were in the mid 40s, and there was a constant wind. My buddy, who was also on the trip has the same bivy. Neither one of us had condensation problems, but we did set up under a tarp. Also, despite the cool temps and constant wind, we were toasty under the tarp, and our bivys weren't totally battened down. We used them more or less to add a little more warmth to our cheapo 'patrol' sleeping bags.
 
hikeeba said:
EmsRescueGuy, What sort of bivy do you have?

I also have a $30 "waterproof-breathable" bivy that is more or less a coated nylon sleeping bag cover with a net that zips over your face. I got it last year from The Sportsman's Guide just to try out. I've only used this one on one trip. The overnight temps on the trip were in the mid 40s, and there was a constant wind. My buddy, who was also on the trip has the same bivy. Neither one of us had condensation problems, but we did set up under a tarp. Also, despite the cool temps and constant wind, we were toasty under the tarp, and our bivys weren't totally battened down. We used them more or less to add a little more warmth to our cheapo 'patrol' sleeping bags.
Click to expand...

This is the type i have, also from Sportsmans Guide. I was using it for addded warmth inside a tent over a fifteen year old slumberjack mummy bag. due to my size and the size of the bag the bivy was actually open in several places. I was on a foam mat and was nice and toasty warm all night, my only concern is the aforementioned condensation.

Ps: it was in the low 30s- high 20s with a strong wind coming off A lake. it was very damp out and rained for a short time earlier in the evening and snowed for about an hour that night.


I may try washing the sac, this may reduce its waterproof factor but i mainly bought it for added warmth with a thinner bag for my sar pack.
 
All bivi bags have condensation issues...some are much better than others in mitigating the problem. Gore Tex has been the standard for years and is considerably more breathable than coated nylon but will still have condensation. This week in my military issue Gore Tex bivi I had some minor condensation around my face where I was breathing but it was so minor it didn't cause any problems.

There is newer technology now such as the eVent material as used by Intregal Designs is showing great promise. They won the coveted Backpacker's Editor's award in 2004 for their bivi bags because the material is lightweight, waterproof and extremely breathable. Gore Tex and eVent is spendy so nylon is a lower cost alternative...you just need to make certain your bivi is open in order to vent. Intergral Design now has a newer model bivi out that has a very unique venting system that prevents rain/snow from falling into the bivi but providing max venting.

A bivi will add a least 10 degrees of warmth...the wind blocking functionality alone is worth the investment.
 
If you're willing/able to pay for a higher end bivy like an Integral Designs or Black Diamond (aka Bibler), you might want to consider a small siltarp tent -- see http://www.tarptent.com/ -- like the Virga or Contrail model. Just about as light and as easy to set up as an ultralight bivy, and it will resolve the condensation issue by keeping your shelter from coming into contact with your bag. Henry Shires and his small crew at Tarptent are great folks, and can customize your tent if you have ideas. My gal and I have been using an original Cloudburst for three years now, and it's a charm. Two minutes to set up, with sewn-in floor and bug net. -Glen
 
I've been using the Guide Gear bivy for about three years now and I haven't had any problems with condensation. My typical kit is a tropical weight bag or poncho liner, bivy, poncho and cord. This set-up has worked very well for me even in some really bad downpours in Brazil.

In decent weather I don't zip up the hood. When I do I have the same accumulated CO2 problems mentioned above. I notice it when I start to yawn excessively. Unzip and get some fresh air and it goes away instantly, then I fall asleep.

I haven't used them in really cold weather but might get the chance in the next few weeks (I'm in the States now for a month). Condensation might be worse in the cold but I can't say.

In all I've been very happy with my cheap bivy's from Sportsman's Guide. If I set up my poncho correctly over the head area the whole set-up keeps me dry and cozy. Mac
 
You must log in or register to reply here.
Back
Top