I love the mighty lite line from columbia. The omni heat lining is the main reason. The vest itself is very thin, you would never think that it could keep you warm but the secret is the lining which works like wrapping a baked potato in aluminum. the heat you make gets reflected back to you and thus you're warm and cozy. I use it for running mainly because i hate being bulky and i really appreciate the pockets. It's form fitting but true to size.