That's why you wouldn't use a vapor barrier with wool (or Thinsulate). Any material won't dry out in the bottom of your pack, most packs act like a vapor barrier and aren't breathable, although wool will develop less to no mildew compared to the other options and prevent your pack from mildewing as well. I've certainly made that mistake and have smelled the results. ? A piece of foam board in a wet pack would also be bad and show what happens when moisture gets behind vapor barriers. That's wool's strength though, controlled moisture management (keeps it away from other surfaces) combined with mildew/mold prevention. I also probably wouldn't use wool in the Southeast US, but you're going to get moisture inside any wall, especially many DIY vapor barriers using any tape. If you can panel (not basic plywood) and properly caulk, that would probably be the superior option for both R-value and moisture build-up. I'm interested in how wool does in a moderately humid environment like the PNW which I spend a lot of time in year-around. I'm also going to use a breathable, but water resistant layer over my insulation to trap air, slow down moisture absorption, and then help with drying things out.
Wool, as well as things like Polar Fleece keep you warm (wet or dry) because they trap air in the material itself, not just next to the skin, and don't collapse when soggy. All insulation works this way to some extent, the combination of the material being insulative (prevent energy transfer) and trapping air. Some don't work when wet, the material collapses (bird down for example) and the airspace disappears. Wool's "crimp" or waviness helps with this and polar fleece mimics crimp. Thinsulate is also supposed to also still insulate when wet, I've had mixed results with it in my backcountry gear vs polar fleece or wool, but that's when saturated. ?♂️
Mineral wool could be an intriguing option, but I would be wary of the majority of the materials (glass & silicate fibers) it's made out of in a small living space. I wonder how bad the silicate versions are? Would be very fire resistant I imagine.
Going through my old notes, the unique negatives of wool, specifically Havelock to consider are:
- Smell, if it doesn't smell when new it was chemically washed and there are +/- to not having lanolin in the wool.
- Moths, they go after natural fibers. Some wool insulation is chemically treated to prevent pests from wanting to eat the natural fiber. Havlock doesn't do this, but lanolin should repell insects so it's a trade off for the smell.
- Cost.
