New Open Box. The Under Armour Base 4.0 Long Sleeve Shirt in youth size YMD is a solid black shirt made from a polyester blend material. It features a crew neck and pullover closure, making it easy to put on and take off. Designed for both boys and girls, this shirt is perfect for active kids who need comfortable and breathable clothing during physical activities. Its long sleeves provide extra warmth in colder weather, while the brand's reputation for quality ensures durability and performance.