Perfection Evolved. Version 2.0 of our premium ultralight has an improved fit that’s more comfortable, mobile, and flattering, with more room in the chest; a slightly longer length for added coverage and warmth; a softer fabric to further enhance the comfort; and a secure drawcord hem to seal out cold and fine-tune the fit.As an ultralight insulating layer, the MicroTherm is thinner than traditional down jackets. But that combination of minimal bulk and effective warmth is what makes it special, and is the result of its patented construction and the exceptionally high-loft Premium Goose Down that it holds close to the body for maximum thermal efficiency. NOTE: Temperature ratings are based on a controlled laboratory test by an independent university lab. Also consider: your sensitivity to cold and wind-chill; time of exposure; activity level; and use of layering.NOTE: As a reference for comparison, we have included the customer reviews of the MicroTherm 1.0 below. Any reviews dated prior to July 30, 2018 are for the MicroTherm 1.0. All reviews dated after July 30, 2018 are for the new MicroTherm 2.0. Models shown are 5’9" to 5’11" tall, wearing size S/4, L/12, or XXL/18.