Within this temperature range, you'll normally need just one layer of clothing. If it's wet or windy, however, you may want to add a vest and some extras. Here's where you'll need two layers. If you're in a snowy area, you should consider investing in a water-resistant jacket. When the temps drop below 10 degrees, you need to be careful.
Perspiration moves more easily through two thin layers than it does through one thick layer.
A well-designed layering system keeps you warm and dry, yet still allows freedom of movement. Which translates to unpleasant running in heavy, damp clothing. You've always heard that you lose more than 50 percent of your body heat through your head. Well, you heard right, so keep your head and other extremities well covered when the temperature dips below 40 degrees. On cold, windy days, remember to cover your face.