I sometimes head out on colder days, and I only wear a jersey underneath, with arm warmers, and a base layer. This vest totally keeps your core warm, while regulating your body temperature. I never feel too hot (I would if I was layering up with a jacket), and I'm also never too cold because I'm always moving and because it also has a windproof membrane. It's brushed on the inside and has reflective trim on the outside, so it's perfect for evening or early morning commutes as well. It is also full of zippers, which is helpful if you want to only take your credit card and keys.