Bivy Question

What kind of condensation are you worried about? Inside the bivy? On the tarp? At those temperatures, condensation on a tarp is obviously frost, and can be wiped off easily. Condensation within the bivy, and particularly within your sleeping bag, is potentially a more serious issue, especially on longer trips, and is often addressed through frequent drying in the sun (if possible) or through some form of vapor barrier.

Two links that should be of some help- one with many ideas on application of vapor barrier techniques, the other on the advantages and disadvantages of tarp/bivy combos.

Good luck,
James

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=17103&skip_to_post=139834#139834

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=18215&skip_to_post=140181#140181

Jaime –

Thanks for the links.

I am worried about condensation collecting inside the bivy.

Here in western MN the wind always blows so I was hoping to keep spindrift off my bag while using the tarp winter camping. I didn't want to shell out a lot of money for a bivy right now so I was hoping to get by with nylon since I don't need a waterproof bivy. If I am going to get a lot of condensation inside the bivy I will take my chances with a little blowing snow for short trips.

Thanks,
Matti

Hard to say. Condensation WILL occur if the temperature inside your bag/bivy drops below the 'dew point'. Whether this happens or not varies on how warm you sleep, how warm your bag is, if you are wearing VBLs, how much you sweat, etc…it can happen inside your sleeping bag even without a bivy if conditions are right.

Matt,

In those temperatures, you can throw together a VB liner with a few garbage bags taped end to end- cheap and easy to experiment with. With a VB liner in place, you will only be asking the bivy to keep external moisture out (rather than also manage internal moisture), so most any material will do. With a VB liner, you won't have to worry about condensation inside the SB or bivy. Might be worth a try!

James

I have used the first generation Lithium with Pertex Quantum inside an Equinox ultralight bivy in similar temperatures (northeast) for up to 3 nights. I use a full length closed cell pad under the bivy with a 3/4 length inflated pad inside, as my Exped Downmat has sprung 3 consecutive leaks and goes flat overnight.

Regardless, the silnylon bottom of the bivy usually has some frost, and there is occasionally some on the underside of the bivy top fabric, but as has been mentioned, this is easily shaken off. For trips of up to four days, I have never had problems with frozen moisture inside the bag- so long as I take care of my feet and breathe.

Your exhalation can cause a good deal of ice buildup around the face opening of the bag- so this is where you want to bivy to protect form internal moisture. Nylon is fine, it is more important to have good coverage around the opening.
Also, I have experienced ice buildup in the footbox- bivy or no. Using plastic bags over liner socks and under down booties or heavyweight socks eliminates this.
With these provisions, I have had good experiences with a plain nylon top bivy in conjunction with various taprs in the Catskills and Adriondacks.

Thanks for the info Michael. I'll have to give the bread bags a try if I have problems this weekend.

I was using my downmat this fall and noticed a slow leak over the course of three nights. I sent it back to OR and they shipped out a replacement. I guess I am getting the new version that doesn't require the billows/stuff sack to pump up so I am anxious to try it out.

It will take a month to get a new downmat, but I think they have addressed the issue with the slow leak.

Thanks,
Matti

Hello Matt,
Just a suggestion. I have tried wearing my shell top and bottom in cold temps 5 deg to 35 deg.nights. And it does seem to be somewhat effective as a VB and has added warmth for me as well. I know that it is not a proper VB, but I havnt had any problems with condinsation on me or the bag for 5 nites . The shell seems to breath enough and you can zip your jacket/ pant legs up or down to add more venting if needed.
Wayne

Thanks James & Lynn!

After reading the thread James shared with me I have decided to pick up a WM Hot Sac to use in addition to the nylon bivy. If used correctly it should take care of the moisture managment problems I have experienced in the past.

Thanks,
Matti

Matti,

I don't have any experience with the Hot Sac. Once you have tried it out, please do share your thoughts with us. One word of advice if you are new to VBs would be to try it out before using it in the backcountry- not even necessarily for a whole night, but just to see how everything fits together in practice, and in particular to figure out how you will regulate your temperature. If you get too hot, the things can be pretty uncomfortable.

Enjoy!

James

If you are just worried about spindrift, then there is a lighter way. Just a single ultralight breathable/water resistant VBL. Several brands out there from 4 to 8 oz.

When I am really concerned about wet, slushy conditions, I use a water proof and "breathable" bivy. But it will capture condensation and the bag will get damp after a couple of days. If there is no sun, then I cannot dry it out each morning. Since all my bags are down, this is a huge problem. Under these conditions, I use a VBL liner. But the VBL is not for everyone. I have used this combo since the '80s and it does work for me.

When camping in sub-freezing temps, I am willing to spend the extra money to get the right (for me) gear.

-Nick

James –

I just went to the one local sporting goods stores that carried the Hot Sac and they had sent them back to WM because they didn't think anyone knew what they were for. Doesn't look like I will get to try it out this weekend. I still plan on ordering one yet this winter so hopefully there are still a few cold nights left this winter. I'll post with how the night went.

I planned on testing the system in the backyard before heading out into the BC.

Nick – I agree. I will be using a 6.5 oz ripstop nylon bivy for conditions well below freezing.

Thanks,
Matt

Matt,

Another option is to duct tape a few trash bags end to end as I did in that thread you read. Trust me, I am not a MYOG expert, my techniques are easily replicated! It was an inexpensive alternative to the Hot Sac, and one that worked quite well. Might be worth a try.

James

I have a vapor barrier liner from Campmor.
I've only needed it once so far and wasn't sure I wanted to spend the gitas for the WM one.

It's about twice the weight and 1/4 of the price, so it might be worth it if you're not sure about VB liners.