I have a lot of Castelli gear.  This fits pretty snug for a jacket.  It''s not form-fitting, but pretty close.  Suppose that''s good to add base layers.  I went over Calaveras (in San Jose) on my maiden voyage and this jacket did pretty well.  High was probably 55 over the top of the hill and this thing kept me pretty snug through the long descent.  Vents are a nice touch for a little ventilation over long climbs.  I did have to unzip the front a couple times to cool off though.  

Oh and who can beat neon yellow camo...

Great fit but it is small on the sleeves if you have long arms great for temp 45 f and up