This article really explains why layering your cloths when going in the outdoors is very important. It explains how to have an outer layer that protects you from the weather and wind, but does not need to provide heat and warmth. A good example for this layer would be a rain jacket. The mid layer provides heat and warmth for the body, like a fleece. It is not expected to be water proof. A heavy sweater or a good fleece would be perfect for this layer because it is think to provide heat. Inner layer is like a base layer. It provides a little bit of heat but mostly is meant to wick away sweat. Under armour is a great base layer.
This article makes me excited to go outside and explore the outdoors. It also teaches me how i should dress next time i go skiing for example.