I just picked up one of these at Costco. I have not had the opportunity to ride the bike with it yet... but I plan to do it this week. It is extremely light weight.. 12 ounces, but I'm stunned by how it helps you retain your body heat. I would think it would be fine down to about 25 degrees if you're being active (cycling) and it is windproof and water resistant. I think with a full zipper in front, you should be able to adjust your ventilation. With it being so light weight, I would imagine that it would not lay on your back if you were riding 10+ mph with it fully unzipped.

Patagonia Men's Nano Puff® Jacket