Under Armour Cold Gear Fitted Mock.  Black.  4-Way Stretch Fabric,  for maximum comfort and mobility.  Duali-layer fabric with warm brushed interior for warmth.    Features Moisture Transport system to keep you warm and dry.   Stretch mesh back and underarm panels for ventilation.  UA item  # 1366066.   Retail price $ 55.00. 

Polyester/Elastane Blend, with anti-order technology built in.  

The most popular,  high performance,  second skin on the market today.