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At SI Workwear, we carry the toughest brands and the best lineup of work clothing in the country. From job sites to shop floors, our gear is made to handle the grind—durable, comfortable, and dependable every day. If you work hard, you need clothes that work just as hard.

Under Armour 4.0 BaseLayer shirt

UA Base 4.0 is a men's baselayer built for extreme cold weather and lower activity. It uses a unique pattern that's designed to trap heat without adding bulk. Think long underwear, revamped for today's top athletes.

  • UA Base™ 4.0 is our warmest yet, locking in your body's heat to deliver extreme warmth in the extreme cold
  • UA Scent Control Technology to keep you undetected in all pursuits
  • Soft, brushed grid interior traps air against your skin, managing your body's microclimate to keep you warm & comfortable
  • Material wicks sweat & dries really fast
  • 4-way stretch material moves better in every direction
  • Fitted: Streamlined fit that’s not too tight or too loose.
  • Style #: 1353349
  • 78% Polyester/22% Elasterell
  • Imported

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