I tried on a small cirrus, too short in arms and length, perfect in the body. I wear a medium in kuiu and the medium in the cirrus is would be close to that. Cirrus seamed warmer mainly due to the wind resistance fabric, also more durable (still a puffy so not bomb proof). I layered it under a north branch and slid right on with out bunching. Kuddos to Firstlite, obviously thought about how new products work with their older stuff. It compresses nicely, actually really nice for a synthetic. I don't think either one is warm enough for a full on winter coat but both can be layered well.