I loved everything about this jacket--the style, the fit, the attention to detail--but it didn't keep me warm. I wore it on a brisk three-mile walk with a fleece and a baselayer underneath when the temp was in the 40s and I was still chilly. Yes, I am one of those people who's cold most of the time but I don't think this jacket would serve the purpose of anyone who's looking to feel warm in winter. The down is quite thin even compared to other jackets in this category, such as the Marmot Venus jacket. Even though Isis doesn't have a zip-in system, this jacket did fit under the Shastina shell I also bought from Backcountry.