4. Insulated Layer: Down feathers or synthetic ‘loft’ material stuffed inside nylon in the form of a jacket and pants, or perhaps a one piece suit (for Vinson or Himalayas). These layers are usually worn at breaks while climbing on a cold day, while standing on a cold and windy summit, inside the tent as a pillow or extra layer over sleeping bag to add warmth. These layers generally resist moisture, but are intended for conditions where any precipitation comes in the form of dry snow.  
  Base Layer 1