Bivy Condensation

[Anne Walker]

Is a bivy more likely to condensate with a bag that is a bit too warm for the conditions?

[Robert C]

Yes.

[David Ure]

Depends on the breathability of the sleeping bag shell, the breathability of the bivy fabric, whether or not you sweat, what the dew point temperature is, and whether you use the bivy under a tarp or not.

There are several factors to consider.

[Eric Blumensaadt]

Buy an eVent bivy sack and be done with it. If you have condensation it will be minimal.

[Robert C]

Do you own an eVent bivy sack? Just curious what made you say that.

[James holden]

The more you sweat the more moisture there is in a system … If you feel too warm vent the bag and zip it up later if yr cold

Event bibies will still get some condensation occasionaly, but short of a dwr bivy anything else will have more

[Travis Leanna]

I have a hard time managing my sweat without a bivy.

There are a lot of factors that will come into play, but as a general rule, any layer you add will increase the possibility of condensation, no matter how breathable it is.

Although eVent fabric is very breathable, you're still inhibiting the transfer of moisture to a certain degree.

[Alex H]

Every bivy I have used and been around has had condensation at some time or another, Event too.

Actually the best I have used (as far as condensation) is an OR Basic bag cover with Gore Dryloft and the worst I have used (I hate to say) is a MLD Superlight with the Momentum top.

[Steven McAllister]

I found if I hang/suspend the top of an over-sized bivy so that there is some air flow down most of the length, you can reduce the condensation even more.
It could be more drafty, but having a dry bag/quilt may compensate.

When I have done this on frosty nights, I tend only see condensation near the top where my breath is the issue. The rest of my bag is bone dry.

[Brad Groves]

If a bag is too warm, you'll sweat more. If you're sweating more, there will be more moisture in your sleep system… a bivy would be likely to get more condensation in that situation.

[David Olsen]

"Every bivy I have used and been around has had condensation at some time or another, Event too.

Actually the best I have used (as far as condensation) is an OR Basic bag cover with Gore Dryloft and the worst I have used (I hate to say) is a MLD Superlight with the Momentum top."

—

This just goes to show, as I mentioned in another post, how
the materials that clothing and bags are made from has only
some to do with how dry things stay.

Gore Dryloft has the same exact moisture transfer as
eVent. It is the same stuff before the eVent is treated
to reduce contamination.

Momentum is basically the safe stuff the eVent and Dryloft
are laminated onto.

So your experiences are caused by other factors.

[David Olsen]

m

[David Ure]

Thanks for the info on fabrics, David. I had no idea about Gore Dryloft. My experience with eVent has been superb with respect to waterproofness and breathability. Can I expect similar results with Dryloft? Thanks!

[David Olsen]

In something like a bivy, results should be comparable. In
a jacket or shoes, where the laminate would be contaminated
with body oils, the fabric would lose it's water proofness
over time, but continue to be breathable and windproof.

Windstopper is also the same.

[David Ure]

That's very helpful info. Thanks Dave.

[Alex H]

"This just goes to show, as I mentioned in another post, how
the materials that clothing and bags are made from has only
some to do with how dry things stay.

Gore Dryloft has the same exact moisture transfer as
eVent. It is the same stuff before the eVent is treated
to reduce contamination.

Momentum is basically the same stuff the eVent and Dryloft
are laminated onto.

So your experiences are caused by other factors."

Thanks for the material info and I always know that other factors are in play. That being said, I have used different bivys for nearly 40 years, as bag covers not stand alone shelters, and generally in similar conditions. The old taffeta topped ones never condensed (that I can remember). The OR with Dryloft has a cottony feeling material and in over 40 nights only 3 times have I had condensation, all near freezing (7% of the time). With the Momentum top, in over 20 nights it has had condensation nearly 25% of the time in temps from 20's to 50's, not acceptable to me.

This is almost entirely out in the open and not under a tarp. On a recent, dry, trip in Southern Utah I used the Momentum top and it had condensation 5 out of 6 nights and my partner used my OR with Dryloft and had a little condensation on 1 night. Temps 24-33 degrees. I have not used Event but have been out with friends who have them and they had ice in there bivy near freezing.

I have a Montbell Dry-Tec bag cover on the way to test this winter, hoping it might be more like the OR but lighter. I am beginning to suspect it may have to do with the cottony type material the Dryloft is laminated to. May have to just sew a silnylon bottom onto the Old OR top and bring the weight down to 10-12 oz. and call it good.

[David Miles]

Breathing inside the bivy causes a lot of condensation.

I have had lots of problems with bivy condensation, so I built my own. I found a fabric that is fully waterproof but far more breathable. I also wanted a bigger and lighter bivy. I can get dressed in it!

The best thing is the vapor transfer in sub freezing temps.

---

David
You are welcome, but …
A posting with a URL to a sales site owned by the writer is commercial, and is not permitted in this channel. Your (other) posting on this subject is also commercial and is being moved to Gear Deals. It is welcome there.

You must give full disclosure that you are a vendor when posting anything like this, and restrict commercial postings (eg with a URL) to Gear Deals.

I have deleted the URL and let this one stand.

Cheers
Roger Caffin
Online Community Monitor
backpacking Light

[John S.]

It looks good David.

Is the floor the same material? I gather it is nonbreathable.

How many stakes out loops?

Is it seam-taped?

Is the bottom right pic loose looking because it is not staked out?

What holds up the foot end? I see one pole at the head.

Is the mid section supported for snow loading?

[David Miles]

I'm new to these forums and I not sure if there is an appropriate place to post a commercial URL.
If there is, could someone direct me to it?
I guess you could just Google it for more info.

[John S.]

You did post it above, but never answered questions and your website had no details at the time : ).

[John S.]

http://milesgear.com/UberBivy.html

[David Miles]

John and all,

Sorry for not posting, but I did not want to offend anyone. Roger did not want me to place commercial stuff on this thread.

I agree since I have been making my own gear for many years and like having a community of people who are willing and able to explore new gear ideas. I have spent plenty of time in a bivy (rescue) and just wanted something better. I thought there was a section (not MYOG) to place this info.

To everyone out there, keep pushing the envelope!
Dave

[Jim Morrison]

According to the proponents if you have a vapor barrier between the sleeping bag and you, somehow, magically perhaps, insensible sweat stops and therefore there is no condensation problem. I don't believe a word of it, but some who have tried it do believe strongly that it solves the problem.

[Steven McAllister]

A vapor barrier would work, but I never got used to the idea of my perspiration collecting inside the vapor barrier.

I would assume you would get quite wet?

Who's done it?

[Jerry Adams]

I got some "fuzzy stuff" from Stephenson Warmilite

Made long sleeve top and pants – base layer

I thought it was comfortable enough but sort of heavy, better to just use my normal clothing

I have read this would work better for longer trips in colder weather, like artic expeditions

[Author]

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