Down insulation – humid conditions

I doubt you will get anything conclusive even now. It depends…

IF your body is generating enough heat and IF you press all the air out of your bag/clothing as soon as you take it off or get out of bed, the moisture retained is usually not significant IMHO. The key is to force all the warm, moist air out ASAP. If you let the air cool, it will condense inside the down which will add up over time. The worst conditions I've encountered are fog/mist which can make everything dripping wet even inside your tent. This is why I always carry a UL bivy bag, even when tarp-tenting.

I think that as long as you have sufficient sun light to dry out your down, you should be fine. If you encounter cloudy skies throughout your hike, then it could be a problem after a couple of days.

-Sid

Try to dry down garments BOTH morning and evening for best results.

Hmmmmm…..So it something one could be stuck with, but that could be manageable via best practices (squeezing hot air out, drying in sun if possible).

Thanks for the tips and comments.

GRT

Adding external heat, a hot water bottle, not only can feel
good but drives moisture from the bag/quilt while sleeping.

I spent 10 days hiking along the Olympic coast with a down
bag and tarp in January. I kept the bag in plastic during the
day. The only time I had trouble, was sleeping in the open
without a tarp one night. I was right next to the ocean in a ravine.
Very humid and cold with blowing mist. I got cold. The bag
didn't absorb much moisture and I think my body heat drove
much of it out.
I slept fine the next night even without
having a chance to dry out the bag. A tarp made a big difference as did not sleeping in the bottom of a ravine.

It's certainly managable. Small amounts of moisture in/on a down bag dry remarkably fast with even a bit of sun and wind.

One thing to think about is the expected temps, warmth of your system, and how close the first will be to the second. During Le Parcour last fall Kevin S and I both had down bags (and I had a down jacket). As the trip wore on things got wetter and wetter (snow turning to rain all day, no opportunity to dry stuff for several days), fortunately they also got warmer and warmer. If night temps had stayed near the edge of our gear's rating later in the trip, things might have been less than pleasant.

Another thing to think about with packrafting is that you'll likely be a bit damp (yourself and your clothing) at the end of every day (if not outright soaked). Both down and synthetic bags will help you dry damp clothes as you sleep, but synthetics will do so without picking up as much moisture (so says my personal observations this year).