>>2262218Down clothing works, yes (just not when wet). Fill power is a measure of fluffiness i.e. how much loft a given mass of down can generate. Higher fill power means less weight per warmth, it doesn't tell you anything about how much weight (or loft) in total there is. If the jacket is super light, it won't be super warm no matter the quality of the down.
Downproof fabric is generally windproof (usually calandered synthetics).
Disadvantage of quilted down jackets, the seams are not insulated and create cold spots. Good down jackets are filled as boxes.
Synthetic isolation works fine. It's generally heavier and less breathable than down, but doesn't degrade as much as it gets moister. There are different qualities, but if you don't care much about weight it doesn't really matter.
