Smartwool Classic All-Season Merino Base Layer Long-Sleeve Blue Striped S. The Smartwool Classic All-Season Merino Base Layer Long-Sleeve offers exceptional warmth and comfort as we spend the day at the resort or adventuring through the mountains. Its lightweight merino wool construction is warm and soft and features a recycled nylon core for long-lasting durability, while raglan sleeves and stretch merrow stitching enhance comfort and freedom of movement.