The down jacket is such a great invention. The tradeoff between warmth and heaviness/thickness of clothing can be a nuisance not only while wearing clothes, but also while travelling in cold weather. The down jacket is desirable for several reasons: (1) it is super lightweight (at least compared to traditional jackets), while still being very warm, and often warmer than alternatives. This makes it comfy to wear, especially when already wearing multiple layers, thermals, etc. This also makes it convenient to for travel, which leads to (2) Portability. It is capable of being folded into a compact cylindrical form, which is easy to shove into a backpack or suitcase – no cognitive cycles needed to figure out how to optimally fold and pack it. (3) Aesthetically appealing design – for all its functional benefits, this is really what makes it as pervasive as it is. If it were an aesthetically ugly, people would be forced to choose between form and function. One still has to do this in some situations where the down jacket would not be the most fashionable option, but on the whole, it comes in styles and colors that allow it to be worn in a relatively wide range of contexts, from casual to stylish.