From the manufacturer

Boys' ColdGear Long Sleeve

We all hate it. That stiff, distracted feeling you get when you're out in the cold. That's why, we built a baselayer that keeps you warm and dry without being bulky or riding up, so you can stay focused all season long.

• Fitted: Streamlined fit that’s not too tight or too loose.
• Dual-layer fabric with an ultra-warm, brushed interior & a smooth, fast-drying exterior
• Stretch-mesh back & underarm panels provide strategic ventilation
• 4-way stretch material moves better in every direction
• Material wicks sweat & dries really fast
• Ergonomic design keeps seams off of high abrasion areas
• Dropped, shaped hem