Fur — you can't beat it. While some of the newest synthetic materials come close, for holding in the body heat; you simply can't beat wolf or coyote fur, for the trim on a parka. When it's really cold (colder than -40*), you can draw the trim fur around your face & still look and breath through it. If you tried this with synthetics, you'd only succeed in creating icicles.
As I recall one of the first artic expeditions brought the latest wool clothing and froze their asses off. Later ones adopted the sealskin garments of the natives and did rather better.