Sunlight is a double edged sword. On one hand, nothing could live without it. It helps regulate mental health as well as catalyzes production of vitamin D and other nutrients. But on the other hand, sunlight can be deadly. Exposure to ultraviolet (UV) radiation is the leading cause of skin cancer globally. The World Health Organization reported over 120,000 skin cancer-related deaths in 2020. In many of these cases, wearing the right clothing could have been the difference between life and death.

What is UPF?

Ultraviolet Protection Factor (UPF) measures how much UV radiation a garment allows to reach the skin. A shirt with UPF 50, for example, projects your skin from 98 percent of UV radiation. ATSM provides a standard for various UPF ratings:

• UPF 15-24: 93.3-95.9%
• UPF 25-39: 96-97.4%
• UPF 40-50+: 97.5-98+%

Wearing the right clothing under the sun is an important step in protecting skin from overexposure to the sun. A 2001 study found that less than half of the 236 common commercially available fabrics offered protection satisfying the European standard for UV protection. Wool and polyester fabrics provided an exceptional rating of UPF 50+, while cotton, linen, and viscose offer little to no UV protection.

And Merino wool was one of the few fabrics that passed all of the study’s tests. A similar study also showed that wool—and Merino in particular—has superior UV protection characteristics.

But that alone isn’t why you should buy Merino wool shirts for summer. 

Is wool good to wear in summer?

Wool stands shoulder to shoulder with several textiles in UV protection. But avoiding a sunburn isn’t the only qualifier of a good summer garment. The garment also needs to be able to keep you cool and dry. And for that, wool has no equal.

Take polyester as an example. For synthetic fibers like polyester, the same factors enabling them to block UV radiation makes them less able to send heat and moisture away from the body.  This man made fabric has excellent UPF, but it’s not so good at blocking other things that happen when the sun is out. Polyester and other synthetic fabrics are not breathable and absorb heat, making the wearer immediately feel hot, sticky, and stinky.

The reason why wool keeps you warm is the same reason why wool keeps you cool, and its secret sauce is in the crimp and curl. Natural wool fibers create air pockets that absorb moisture and transport it from the body, keeping the wearer both warm and cool.  Wool not only does an excellent job at blocking UV rays, but it acts as a natural air conditioner for your skin, keeping the wearer warm during the winter and cool in the summer. Sound too good to be true? Think about what wool is for a moment. Sheep depend on their fleeces to keep them comfortable throughout the four seasons, and these same fleeces can do the same thing for humans, too. Wool is a heat pump for the body. During the warm months, proper wool clothing wicks moisture from the body, taking with it excess body heat. During the colder months, the air spaces in wool trap heat to protect against bitter cold, and it’s able to absorb 40 percent of its weight in water while still keeping the wearer (sheep or human) warm. Whereas with cotton and synthetic fibers, the moisture accumulates in the clothing and absorbs heat from the sun. Wetness, it should be noted, decreases UV protection.

So is wool good to wear in the summer? Our answer is a resounding yes, so long as it’s the right kind of wool. A thick wool sweater isn’t a good choice for summer, just as a light Merino wool crew is a poor choice for a day in the snow.

A quality Merino wool shirt will protect you from overexposure to the sun. You’ll feel cool and unconstricted as moisture is wicked away from your body. And after a day of sweating, your garment won’t stink.

When selecting the best wool shirts for summer, look for Merino. Merino’s finer, denser fibers offer superior UV protection. These dense fibers also allow for thinner clothing without compromising durability. Wool is sometimes treated to enhance its natural UV protection, especially in technical and performance garments. Nui’s organic Merino wool clothing offers the benefits of summerlong UV and moisture protection without any synthetic chemicals, because we believe nature got it right the first time.