I have been wearing this jacket for 2 months when I cycle to work every day. I live in Northern California and the temperature in the morning was around 50-60 degrees - the jacket is perfect as a windbreaker, I only need to wear a t-shirt underneath and there is ample ventilation through the underarm vents. I was surprised how thin and light the jacket is, but how good it is as a windbreaker. I haven't tested it in the rain yet. During the day when it's too hot to wear a jacket, it's very compact, you can roll it up and put it in one of those little bags that fit under a bike seat. Size wise I usually wear medium shirts/jackets and I bought a large jacket - it fits well, not too big and I could probably wear a long sleeve shirt underneath when the weather gets cooler.
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