Speaking of cold weather clothing, the advantages of wool are: 1) up to 30% of its weight, wool both absorbs moisture so it does not evaporate on your skin (cooling); 2) actually generates warmth by exothermic reaction; and 3) resistance to flames and sparks.
The disadvantages of wool compared to polyester fleece or batting are: 1) significantly lower abrasion resistance and tensile strength (wear and tear); 2) greater weight for a given insulation value (insulation = trapped 'dead" air); 3) significantly harder to get dry when wet; 4) above 30% by weight, more moisture absorbed leads to sharp drop in insulation value; 5) much more difficult to maintain in the field; 6) stink when wet (Doesn't bother me.); and 7) skin irritation for some users.
(Polypropylene is an obsolescent skin layer that is famous for "Polypro Stink," a problem unknown to polyester (provided you have access to detergent and water)' "Polypro" is also infamous for melting at normal clothes dryer temperatures.)
Balancing those factors, wool is often the choice for socks. For all other applications, all Arctic and Antarctic expeditions, except those from New Zealand use polyester fleece or batting for insulation layers (See comments on objectivity of Polartec above and consider all those herds of sheep in NZ.).
I remember when the above judgment became almost universal. Suddenly, we had all these wonderful German and Swedish wool military surplus trousers and shirts on the market cheap. Those days are long gone. The supply is much more limited and the prices much higher as the supply dried up due to first-world militaries shifting from wool to polyester and nylon (outer layers).
As to down, you perspire all the time as your body attempts to maintain 100% relative humidity next to your skin. Conditions of activity, relative humidity, temperature, sun, and wind mediate how much you perspire. In cold weather, the warm, moist air created by body heat and perspiration migrates outwards until it reaches "dew point," at which location water vapor becomes liquid water. That location is more and more likely to be closer and closer to your skin as the outside temperature is colder. This means condensation inside the garment - be it a coat or sleeping bag. So if you do not have access to good drying conditions, a down garment steadily absorbs the water and steadily loses its insulation value when worn. This is true regardless of any other factor. It is not at all unusual for a sleeping bag to lose 1/2" of total loft a night.
So when I was backpacking a lot in California and elsewhere in the West, down was a fantastic choice. Down garments, including sleeping garments, went on a rock in the sun every morning and whenever needed, and all was well.
I arrived in Ohio and have used my beloved down bag outdoors once in thirty-five years. The lumps were palpable the first rainy morning and Saturday night was not comfortable.
Turns out down is difficult to dry out in the field when it is overcast and damp day after day. Polyester, being hydrophobic, does not absorb water into the fibers and has a much reduced problem with condensation as a result, especially the upper-scale polyesters that are silicone coated. In extreme conditions, such as a sled run to the North Pole, collection of ice inside polyester bags required air drops of replacement bags. Nothing can stop physics. Still, you want condensation inside a polyester garment not a down garment (except in unusual circumstances) and Eddie Bauer cannot stop that condensation.
