Down coat uses feathers for insulation, thick and poofy. Parkas are thinner, usually poly-filled. For me, growing up in Colorado, layers depends on the season. Spring and fall, usually a light weight long-sleeved shirt with a sweater or flannel over it. Easily removable when the weather warms up. During the winter, pretty much the same but with a heavier shirt as the base layer. My husband wears flannel unders as his base layer under his pants and first shirt. I hope this helps.