Trapped air keeps a body warm. And wearing layers of clothes creates additional air traps.
Few people know that better than researchers at the U.S. Army Research and Development Engineering Center in Natick, Mass. their job to design uniforms for soldiers to wear in both extremely warm and cold conditions.
Just in case you plan to spend a lot of time outdoors this winter, here are the center's recommendations for the layers of clothing you can put on to stay comfortable at temperatures ranging from degrees above zero to 60 below.
For the coldest weather, start with long underwear made of heavyweight polypropylene. Then add bib overalls and a shirt of polyester pile.
Over these go quilted pants and a jacket liner filled with a synthetic insulation like Du Pont's Hollofil or Polarguard, made by Hoechst Celanese Corp.
Next, a pair of pants in a cotton and nylon blend. Then top everything with a nylon shell and rain pants that use Gore-Tex or a similar laminate.
Neil Smedsted, the chief of the center's life-support clothing and equipment section, said, "Depending on the weather or your activity level, you just adjust the layers accordingly."