Because of their lack of arms, many people don't think vests play an important role in warmth management. However, they are often more versatile than some traditional winter jackets. Vests can be used for temperatures that are cool but don’t necessarily require thicker winter jackets. Vests also grant freedom of movement for your arms while keeping your core (where all your vital organs are) nice and warm. Vests can serve as the outermost layer over a mid-layer or act as a mid-layer themselves.