Different weights are available depending on conditions and activity level. Choose lightweight or medium for moderate conditions and expedition weight for extreme cold or less active endeavors like ice fishing. Add sock and glove liners for feet and hands to complete the base layer. The second layer should preserve body heat and insulate against the cold. One of the best materials for this is fleece.
Fleece offers several advantages over traditional fabrics.
It is lightweight, warm, and very soft against the skin. Unlike cotton or wool, it absorbs little moisture and dries quickly. It also insulates when wet. Most manufacturers produce three weights of fleece outerwear to cope with a variety of conditions. Some fleece treated with a wind resistant coating enables it to function as an outer shell in milder conditions.