After a 3-hour ride in steady rain the O2 jacket kept me totally dry
except along the zipper. I had a nice racing stripe down the front of my wool shirt.
You'll definitely want to size up if you plan to use this as a winter jacket. It has a very snug fit and a rather short sleeve length.
Otherwise, this jacket is a steal. It does a decent job keeping you dry, it's light, it's inexpensive, and it packs down to a hearty pancake.