So light... its not there
First, love the beehive color.
Second, great fit (5'9" 150 lbs) Medium is great, enough room for layers under, but not baggy.
Third- Super light: lighter, thinner, and more packable than my fleece!
Forth- warm! Wore this out three days ago on San Antonio (temps around 18) was comfy with only a long sleeve synthetic T-shirt underneath and a hard-shell (no insulation) over top. Great thing was, that unlike the fleece that this replaces I never got hot. Again, wasn't cold when I paused for snacks, and wasn't too warm when I started off again.