Is humidity/fog enough to completely collapse down loft?

I can't afford to wait on dry settled weather or i would never get out. You get used to rain and mist in Scotland:)
The longest i've used a down bag for in damp conditions is 9 days. It rained at some point every day, and all day on one of them. The ground was continously wet. The outside of my bag got damp from condensation, and i noticed a slight loss in loft. The bag was a Rab Quantum Endurance 250 and i'm convinced that the Endurance coating is a big help in damp conditions. The fabric is starting to lose it's WR though, as it is losing it's loft quicker now.
I've just ordered a Nunatak Arc Specialist with an Epic outer as my first ever quilt, and i hope that Epic performs as well in damp conditions.

Down gear? It works – but just be careful…

I have done 30 day camping/mountaieering trips in the north cascades- and it rained EVERY day, all of 'em, 30 days in a row. THis went WAY beyond humidity and fog. The bag NEVER completly collapsed. THere were a few nights when I noticed it was thinner than usual.

I was careful, dried it when I could, and it was FINE.

It was an 800 fill FEATHERED FRIENDS bag with a non-gore outer fabric. We were in tents.

It lost a little on the wetter days, but I found that hanging the sleeping bag out to dry, when ever I could (in the wind was helpful) made it all okay.

Also, if you have a tent, hang the bag in the strings (loft) as soon as you wake up in the AM. Keep the tent super vented, all the time.

During travel, pack the bag in something waterproof. A plastic bag is fine.

peace,
M!

During the rainy season here in the mid-atlantic, we'll often have continuous light rain with 95-110% humidity for 4-5 days at a time. For instance, the weather forecast for this weekend is for 95% humidity and .3"-.9" of rain per hour from Thursday through Tuesday. There are two hours that the hourly forecast expects the rain to stop, but they still expect over 90% cloud cover so I'm not sure I can count on it.

I've always used synthetic sleeping bags and just got into down. Would relying on my down bag be safe in these conditions ? Or should I expect it to loose a lot of warmth ? If my down bag does lose a lot of warmth, would leaving the tent set up and letting it dry inside the tent work – or would the 95% humidity prevent the bag from drying enough to become warm again ?

ps: I'm planning on using a single wall tent (SD lightning pitched without the inner net tent). Or a tarp if I can get away with it (15-20mph winds that will be shifting 120 degrees during the night), or both parts of double wall tent if I have to. (I'm hoping for advise in the other thread I started about single wall tent suitability).

Thanks.

I doubt your bag is going to dry much in 95%+ humidity unless you are in it to generate heat. You could try rolling the bag up immediately after you get out of it and storing it that way until you need it again. This will purge most of the warm moist air from the bag before it has a chance to cool and precipitate in your bag.