Sleeping in foggy nights

Javier,
No sleeping bag, even with the new glued seams & synthetic fill, will keep you dry outside on foggy nights. That's asking too much of any fabric, save perhaps eVent. But no bags are covered W/eVent.

Stay in your tent and enjoy feeling safe and dry. Just don't vent it too much or the fog can come in. Your body heat will keep the tent warmer than outside air so there WILL be more inside condensation than usual. Don't bump the tent walls if possible.

In the morning, if you have a double walled tent, very carefully remove the fly (so it doesn't touch the tent body) & shake the underside condensation off. If you have a single wall tent carefully wipe of the condensation from the inside W/ a towel.

Eric

Eric,

Feathered Friends has eVent as an option for their sleeping bags or their web site lists it.

Hi Javier,

I agree- good choice to be in your tent rather than under the stars in your bag.

I think you'll find the VAPR bivy to be perfect for nights like these but if the fog is very thick, I'd recommend a tarp over your bivy (this is a setup I often use with my VAPR- no tent). Some great articles on this site regarding the use of a bivy and tarp. Of course, you are safe in your tent.

By the way- eVENT sleeping bags are available- I have one. http://www.featheredfriends.com/ Great bag but it's a bit heavy. These days I prefer the versatility of a seperate bag and bivy.

Have fun!
Doug

But if you have an overwhelming desire to sleep under the stars (even though you can't see them because of the thick fog rolling in)… there are quite a few bag options:

Bags:

1. eVENT bags as mentioned above
2. Sierra Designs bags made with "DriZone" fabric
3. Big Agnes "Shield" series – seamless, waterproof and breathable bags

MontBell also makes a very lightweight waterproof/breathable "protector" for your regular sleeping bag.

Hi Javier-

Wow, 7 foggy nights is going to be tough on a down bag no matter where you sleep. You're going to get the double whammy of external condensation from the fog, plus the high vapor pressure of the foggy ambient air will reduce the vapor pressure gradient from the inside of your bag to the outside, making it harder to dissipate moisture from your perspiration. This is a recipe for turning your fluffy down into wet oatmeal by the end of your trip. :(

A bivy sack is not likely to help this situation. Though, like Doug said, a very breathable bivy like the Vapr bivy used with a tarp would be my choice if you didn't want a tent.

I agree with Eric — this is a good case for a double walled tent. Try to isolate the condensation from your bag and increase the temperature above the dew point inside the tent. You could even try lighting a candle in the tent to help dry things out.

Finally, you might consider a synthetic bag for prolonged use in fog.

Cheers,

-Mike

Doug,

Could you elaborate on when you choose to pitch a tarp or not? I just bought an eVENT bivy (ID Bugaboo) that is supposedly stormproof. As such, I am planning to leave the tarp behind for most outings. I can foresee needing a tarp for snow, steady hard rain, and fog, but not for much else. Am I missing something?

Sorry for hijacking the post, but this has been a burning question for me lately, and seems partly relevant given the fog use.

Also, any news on when VAPR bivies will become available again?

javier I have two BMW bivies (nano and normal) and they can´t resist rain (heavy or light)

But in foggy conditions this bivy works well but its impossible to avoid some condensation.

check this topic if you need more info (in spanish) about the vivy

http://www.madteam.net/foro/ver.php/tecnica_21179.html

Javier, I agree with Michaels analysis.
It does not matter what fabric you choose, at 100% relative humidity the only vapor pressure differential would be due to the higher temperature inside the bag, and the moisture would condense when it reached the dew point, somewhere in the middle of your bag insulation probably.
This is a classic case where a synthetic bag is preferrable. I came to the same conclusion for a future hike on California's Lost Coast. I recommend a pertex shell synthetic bag such as the Snugpak Softie. 800 grams, good to 0'C with an insulation layer.

http://www.snugpak.com/20_outdoors/21_05_micro.htm