Clothing in layers is an effective way to keep warm in cold weather because it adapts to the different conditions on a hiking trip. When you exert yourself like when you’re hiking, your body temperature rises and naturally you sweat. The base layer should be able to quickly wick away any moisture so that you don’t get wet. That’s why it’s important that you don’t use cotton shirts as a base layer because they absorb moisture. When you’re resting, your body temperature can go down too quickly if you’re wet and it’s difficult to keep warm. Wool and synthetic clothing works great as a base layer.
You should also have a middle layer that’s meant for insulation and on the outside something to protect you from the rain. Watch the video below for more details.