Are you always cold? If so, a down jacket could be for you. Down is the best natural insulator (collected from usually ducks or geese), offering unmatched warmth-to-weight ratios and awesome compressibility. However, since down doesn’t perform too well when it’s wet, it’s best to find a jacket that has a waterproof or water-resistant outer shell, to keep it from losing its loft. Another thing to consider in your purchase is the fill power. The fill power number, usually ranging from 500-900, and going up in increments of 50, is the measure of how dense the down is, and, therefore, a jacket with a higher fill power number is usually going to be warmer. Finally, some jackets will indicate what the ratio of feathers to down is; lower quality jackets will have more feathers, so a ratio of say, 75% down to 25% feathers is a good starting point.