Rothco Gen III Level I Underwear Bottoms are part of ECWCS (Extended Cold Weather Clothing System) which provides extra warmth in cold climates.

Product Details: 

Level 1 Of The ECWCS
Silk Weight Underwear Bottoms Are 100% Polyester And Wick Away Moisture
Anti-Microbial Properties Help Protect Against Bacteria
Anti-Odor Prevents Bad Odors
Features An Elastic Waistband And Access Fly