My new favorite jacket is my Patagonia Micro Puff Hoody, which the brand says is the most thermally efficient synthetic hoody they’ve every made. It is ultra light, stays warm when wet and folds up into its own pocket—which can double as a pillow on a plane or in a car.  It’s also easy to stash in a carry on or backpack when heading from cold  climes to warm or the other way.  It’s not inexpensive ($299) but also can work as a layer, allowing you to leave home that bulky sweater or fleece.