A base layer should fit as close to the skin as possible without being so tight that it restricts movement. The purpose of a base layer is to wick moisture away from the body to keep you dry and warm, which is much more effective if it fits snugly against your body. Our base layer tops are slightly longer to prevent cold drafts, so they don't gap at the back, keeping cold air out. For the same reason, base layer pants or long johns often have a high waist, which also helps them stay in place without sliding down.
The warmth of thermals depends on the material and thickness. Wool is generally warmer than polyester, and the thicker the material, the warmer the base layer. The design also plays a significant role in retaining heat. For example, the inside of the fabric can be brushed or have a waffle texture that better traps warm air. A higher collar or an integrated balaclava can also help prevent cold air from reaching the skin.
Base layers made with synthetic materials like polyester are very durable, stretchy, and quick drying. They have good moisture-wicking properties and dry quickly, keeping you dry and warm. These base layers are excellent for intense activities.
Base layers with wool have good temperature-regulating properties, meaning they keep you warm when it's cold and cool you down when it's warm. A set of base layers with wool is ideal for activities with varying intensity, such as downhill skiing, where you alternate between intense runs and sitting still on the lift. Merino wool is often used in base layers because it is softer against the skin and doesn't itch like regular wool.
Base layers made of a blend of wool and synthetic materials give you the best of both worlds! Synthetic materials tend to start smelling after a while. Here, wool's antibacterial properties improve the performance of the blended material. Wool can be sensitive to wear, but polyester makes the base layer more durable and easier to care for when washing.
