A thermal base layer is a type of clothing designed to provide warmth and insulation while wicking moisture away from the skin. Typically made from materials like merino wool, synthetic fibers, or a blend of both, these layers are worn directly against the skin. They are essential for outdoor activities in cold weather, as they help regulate body temperature and keep the wearer dry. These base layers come in various styles, including long-sleeve tops and leggings, and are often used in activities such as skiing, hiking, and snowboarding. Choosing the right thermal base layer can enhance comfort and performance during cold-weather adventures.