Many people make the mistake of thinking wool is only supposed to be worn when it is cold outside. While it is true that standard wool in the form of a thick sweater is ideal for cold weather, Merino wool can be worn anytime regardless of the temperature. Much of the warmth is dependent on the micron size (see What’s in a Micron? for more detail), generally, the larger the micron the warmer the garment.
The reason wool is comfortable to wear in both warm and cool climates is because it is a highly absorbent fiber. When the air is cool and damp, wool absorbs moisture and keeps a layer of dry insulating air next to the skin. When the air is warm, that same absorption capacity funnels away perspiration and keeps insulating dry air next to the skin. This makes the body’s natural cooling system perform at an optimal level.
In fact, the same absorbent properties that help keep you cool in the summer also helps keep you warm in the winter. Merino wool can absorb up to 35% of it’s own weight in moisture which creates lower humidity in the area directly next to the skin making your body better at regulating internal temperature regardless of external temperature changes.
I don’t know about you, but I don’t enjoy a wet cotton t-shirt or any other synthetic material for that matter around my body when I’m perspiring in hot weather. It’s not only uncomfortable, but it leads to chafing and a downright smelly ass shirt.