Pearl Izumi Select Barrier windbreaker. It isn't rainproof, just mildly resistant to mist. But it retains windproofing even when soaked through, including when my shirts are soaked. So it's still comfortable even in chilly wet weather. It's reasonably close fitting, about like the clear jacket shown above.
Rolls up into its own rear pouch/pocket, and even smaller if packed into a quart sized ziplock bag, squished to expel excess air and zipped closed. Fits into a jersey pocket. I usually carry it autumn-spring on every ride in case of rain or I'm out after dark when it cools off quickly. It's been comfortable even below 20F on dry winter days with a baselayer and long sleeve jersey, after I'm warmed up.
In comparison I have a Shimano Storm Jacket, completely rainproof, windproof, etc., double lined with supposedly breathable fabric (it ain't) and with a mesh liner. Even with a cape it's still not as well ventilated as I'd like for cool weather, so I end up just as wet from perspiration as with the Pearl Izumi windbreaker. It's best for cold winter rides, wet or dry, with wicking layers to stay reasonably dry.