Down insulation offers a better warmth to weight ratio and is very compressible. Therefore, it’s perfect for demanding hiking trips where every gram of equipment carried influences your performance and you only have limited space in your backpack. The biggest downside of down insulation is that it gets flat when exposed to water/moisture and thus loses its ability to entrap the body-warmed air and keep you warm. Furthermore, down insulation takes more time to dry then synthetic insulation. These drawbacks are alleviated, but not eliminated if the down has been treated.
The main advantage of synthetic insulation is that it does provide warmth even if it gets exposed to moisture and water, but there are also disadvantages; it is heavier for the warmth it provides than down and doesn’t compress as good either. In dry conditions, a high-quality jacket with synthetic insulation performs similarly to a goose down jacket with a fill-power of 600 – which is a rather mediocre down quality compared to the 800-fill-power down jackets reviewed above.