I'm a little confused now. I always thought the whole point of sectioning a sleeping bag was to stop its contents (in this case down) moving all over the place, is this not the case? Who makes bags where this is a problem? Or have I got the wrong end of the stick (happens all the time to me :icon_redf )?
I agree that if anything is wet, you are going to be cold. Doesn't really matter what material it is. Insulation works because it has low thermal conductivity, loft is important because air is a good insulator, the reason down is warm is because air pockets exist both within the feather (used to be blood vessels when the feather formed) and surrounding the feather. If you compress it, you have less air and therefore less insulation. However, 5cm of compressed feathers would act like 5cm of uncompressed lofted down as the thermal conductivities are almost the same (0.034 W/mK for feathers, 0.025 W/mK for air at sea level, (all measured at 300K), for those who do not know what thermal conductivity is, the lower the number the better the insulator, (i.e. aluminium 237W/mK, copper 401W/mK)). It may interest you to know that pure water is an insulator (0.561W/mK), its the minerals dissolved in it that causes it to conduct.
Greg
I agree that if anything is wet, you are going to be cold. Doesn't really matter what material it is. Insulation works because it has low thermal conductivity, loft is important because air is a good insulator, the reason down is warm is because air pockets exist both within the feather (used to be blood vessels when the feather formed) and surrounding the feather. If you compress it, you have less air and therefore less insulation. However, 5cm of compressed feathers would act like 5cm of uncompressed lofted down as the thermal conductivities are almost the same (0.034 W/mK for feathers, 0.025 W/mK for air at sea level, (all measured at 300K), for those who do not know what thermal conductivity is, the lower the number the better the insulator, (i.e. aluminium 237W/mK, copper 401W/mK)). It may interest you to know that pure water is an insulator (0.561W/mK), its the minerals dissolved in it that causes it to conduct.
Greg