This vest is such a great item! I have worn it to work for some added warmth in my chilly office, but i have also used it to add warmth on a cold day out on the slopes or for showshoeing. It is fashionable yet functional. I usually wear a medium in Patagonia products and a medium fits perfectly with this item. It is slim fit, but that enables you to use it for layering. The vest fits well over a mid-weight base layer, with a jacket over top.