Lisa, I have the jacket and wear it when I go running. It's a nylon fabric--not fleece--and is very lightweight. I'm assuming that the vest and jacket are the same fabric. Perfect for a top layer. I've worn it in below freezing temps on top of a base and mid layer, and I've been quite toasty. You can't beat it for visibility, which I'm sure you know since you have the jersey.

I have been tempted to put the vest on my Birthday wish list. If you decide to buy it, could you please post a review?