The Marmot Polartec Base Layer Top Shirt in men's medium size and blue color is a thermal long sleeve shirt made of 100% polyester fabric. It features a pullover closure and is machine washable, making it suitable for activewear. Ideal for winter and fall seasons, this shirt is perfect for activities like walking, cycling, hiking, skiing, and running, providing warmth and comfort during outdoor adventures. The solid pattern and regular fit make it a versatile and stylish option for casual wear.