Question about bivy's and condensation

[Caleb]

Hi Folks. I'm trying to improve, simplify, and reduce. For years now my sleep system has been siltarp and a goretex bivy bag/down sleeping bag combination. This combination is lightweight and has afforded comfort and safety in a wide range of conditions...I like knowing i can stay bone dry in torrential downpours and when camped on soggy ground. The only drawback to this is that in very cold and wet weather the bivy traps more condensation than I'd like it too. To counter this tendency I use a VB liner, which helps significantly, but I'm wondering if the bivy material itself could be improved upon, or if maybe I should consider buying a new bag with a tougher microfiber shell (or dryloft) and forgoing the bivy altogether? Any suggestions/advice? Is there a better material than goretex for a bivy, such as epic or eVent? I love the waterproofness of goretex but I'm tired of dealing with the condensation. thanks C

[orangebug]

Any shelter will have condensation. If you only used the you would still get condensation, especially over your head. You reduce condensation with the VB, but that leaves you a bit more wet and stuffy.

The biggest problem to condensation is getting "rain" on your bag. I use either a hammock or a Wanderlust Nomad. As long as I keep from touching the walls, the condensation from the Nomad is minimal. I've been impressed with how little condensation is associated with either a Hennessee or Speer Hammock.

[The Will]

I am aware of two schools of thought regarding the condensation issue and bivy use.

The first states that if you have a sleeping bag with some sort of water resistant laminate shell (Dryloft will serve as general example) then it will not be possible for your body heat to keep that moisture in its gaseous state and drive it through two such layers...the Dryloft layer of the outer shell of the sleeping bag and then the Gore-Tex layer of the bivy. The result will be condensation on the inner side of the bivy and subsequently on your bag.

The second hypothesis is that it makes no difference what the outer shell of your bag is made out of. Back country travel, even in summer, often takes place at higher elevations and/or northern lattitudes where the temperature can approach freezing twelve months a year, or at the very least, become significantly cool at night. Warm moist air will exit your sleeping bag, hit the cooled bivy layer and than condense.

I subscribe to the second hypothesis (irregardless of sleeping bag shell material, during very cool to cold nights there will be the possibility of some condensation). Aside from the use of a VBL, the best strategy in my opinion is to accept the condensation while also being prepared for it. For bivy use, I believe it is a fine idea to have some sort of water resitant shell. You mention buying a bag with a "tougher" microfiber shell...if your current bag has a microfiber shell than I would think that adequate. I have bags with Dryloft shells or a generic form. These work fine for me and I believe that the case against these types of shells not being breathable enough is way overblown.

Two things to keep in mind: 1) it takes some kind of catastrophy for a down bag to be soaked so some condensation won't hurt and 2) whether your bag is down or synthetic it will accumulate some humidty and thus it will be ideal to let it get some sunshine every fourth day or so. I mention these as a way of saying that even if your bag gets a bit wet with some condensation and you have to lay it the sun for awhile, well that should be done on occasion anyway.

[Caleb]

Two things to keep in mind: 1) it takes some kind of catastrophy for a down bag to be soaked so some condensation won't hurt and 2) whether your bag is down or synthetic it will accumulate some humidty and thus it will be ideal to let it get some sunshine every fourth day or so. I mention these as a way of saying that even if your bag gets a bit wet with some condensation and you have to lay it the sun for awhile, well that should be done on occasion anyway.

This is my practice now, but it's still a pain in the butt. I'm going to be researching the merits of the various shell materials (microfiber/dryloft/etc) and try to come up with a way to eliminate the bivy altogether for most of my camping situations. I know for sure that gortex doesn't work as a sleeping bag shell...for all its vaunted claims, in practice it's just not permeable enough to vapor. when it was tried this way in the past, down bags always wound up getting wetted out. But gortex IS very waterproof. What is your experience with dryloft? how well, for instance, can it hold back the water pressure from soggy ground or a rivulet of rain water?

[Jaybird]

Hi Folks. I'm trying to improve, simplify, and reduce. For years now my sleep system has been siltarp and a goretex bivy bag/down sleeping bag combination. .....etc,etc,etc,

Yo Caleb:


I've owned a Kelty Dart-2 (Bivy-style tent..less than 3lbs) for 3 years now & have never had any problems.

If you're wanting to "lighten up" the load....theyre the way to go...just use
you're vents...air-flow is very important in close quarters....

[fantasmagris]

I made a bivy with silnylon floor wrapping up the sides and foot a few inches, the top is a very light 0.8 breathable nylon with a DWR finish. It aso has a large non zip opening and a removeable mesh hood for that. Condensation is almost nonexistent. Of course, the trade off is a small tarp must be used over the top.

[The Will]

This is my practice now, but it's still a pain in the butt. I'm going to be researching the merits of the various shell materials (microfiber/dryloft/etc) and try to come up with a way to eliminate the bivy altogether for most of my camping situations. I know for sure that gortex doesn't work as a sleeping bag shell...for all its vaunted claims, in practice it's just not permeable enough to vapor. when it was tried this way in the past, down bags always wound up getting wetted out. But gortex IS very waterproof. What is your experience with dryloft? how well, for instance, can it hold back the water pressure from soggy ground or a rivulet of rain water?

My experience with Dryloft has been very good. I have read of people preferring something with more breathability, however, I don't find this to be the crisis situation some make it out to be...again keeping in mind that any bag will accumulate humidty regardless of insulation type or shell material. To counter this a bit, as soon as I get out of my bag in the morning, I stuff it. This process "emptys" the bag of the warm moist air that would eventually condenense if left to cool. Also, it seems to be the most convenient time to stuff your bag as your wouldn't have to get back in your tent to perform this chore...but this a digression from your question.

I've appreciated having the Dryloft shell because there are plenty of occasions when I may be sharing a tent with a friend and they have done an inadequate job of seam sealing or I'll be up against the wall of the tent or snow cave and get lots of condensation on the bag...many scenarios all of which have made me appreciate that Dryloft shell. Regarding what you specifically ask, water pressure from soggy ground or a rivulet of water, those types of direct contact with water that involve pressure or a continuous stream (rivulet) I would say are too much for any sleeping bag shell. But if you were under your tarp and it was snowing and you got some wind-blown snow on your bag or even if the foot of your bag was exposed to falling snow, that's a situation I believe Dryloft could handle.

Since were discussing situations involving an inordinate amount of water, let me add that for these unfavorable conditions, bags constructed with tuck stitch baffles offer an advantage as there is no thread visible to wick moisture.

These are my perspectives, hopefully you can glean from others on this board and arrive at a balanced, informed conclusion.

[Whistler]

There are a number of bivies available that are similar to fantasmagris' homemade model. Companies like Oware, Bozeman Mountain Works, Equinox, and Mountain Laurel Designs all make models with waterproof bottoms and water resistant, highly breathable tops. You might want to investigate their offerings, which I think will be lighter and more breathable than what you currently use. I have some experience with the Equinox model, and I've been pleased with it.
-Mark