Beat the Heat – UPF Ratings Explained

Reading Time: 4 minutes

What do you normally think about when you’re planning for a sunny outdoor mission? 

My first thoughts are usually about the weather, the plan, the altitude, and what gear to bring. Then I grab the right pack out of storage and arrange my things in a way I have done many times before. I set out my favorite sunscreen, sunglasses, hat, and whatever gear I might need for the day. Just as important are the clothes I decide to pack. That decision can easily make or break my day.

What is UPF Clothing?

When considering your clothing for a hot day you want something breathable and light but you also want something that is going to hold up well against the sun. The fabric and color you choose affects how much UV exposure you are going to get during your adventure. Bright colors and thicker fabrics absorb more UV rays than fabrics with a low thread count and light colors.

The Ultraviolet Protection Factor (UPF) indicates the amount of UV radiation that will reach your skin through a specific fabric. Lower UPF values mean more UV rays penetrate the fabric, and higher UPF means less UV penetration. Here is a breakdown of UPF ratings:

  • UPF 5-15 allows between 1/5th and 1/15th (20% – 6.6%) of UV rays through the fabric to reach the skin
  • UPF 25 allows 1/25th (4%) of UV rays through the fabric
  • UPF 50+ allows 1/50th (2%) or less of UV rays through the fabric
A trail runner runs through sunny woods in a bright colored long sleeve t-shirt that blocks UV rays.

Ultraviolet Rays – the Good, the Bad, and the Ugly

There are three different types of UV radiation: UVA, UVB, and UVC. UVA rays have the longest wavelength and make up the majority of solar radiation entering the atmosphere. UVB rays are more powerful but have a shorter wavelength and are mostly absorbed by Earth’s ozone layer. UVC rays are completely absorbed by the atmosphere. UVA and UVB rays impact skin cells differently but both are linked to skin burning and development of skin cancer. When shopping for sunscreen look for products that offer broad-spectrum protection because they protect against both UVA and UVB rays.

There are many factors that affect how much UV exposure you will receive. Things like scattered clouds and the sun’s reflection off water or snow can increase your exposure—whereas heavily overcast skies will reduce it. For all the mountain climbers out there, you already know that altitude also plays a major role in sun exposure with harmful UV rays increasing as altitude increases.

The UPF of clothing does not necessarily dictate whether you are going to get burned or not. If the fabric stretches or gets wet it will increase the amount of sun exposure you receive regardless of the UPF. Adding SPF 50+ sunscreen on your face, neck, and arms will help reduce that risk. Hats, polarized sunglasses, and staying hydrated are also very helpful. Although sunscreen should always be used on high exposure days, clothing with a high UPF rating will do great work on your behalf. Unlike sunscreen you do not have to reapply UPF—a good sun shirt will protect you all day.

Local guide getting out on the river using a bright colored sun protective shirt
Local fly fishing guide wearing a bright colored sun protective shirt.

Why Time Matters

In the northern hemisphere the summer solstice is the day when the sun’s energy is at its peak for the whole year. Therefore the spring and summer months before and after the solstice have the highest levels of sun exposure. 

On a more micro level, if we are talking time of day, midmorning until about 4pm is prime time for sun exposure. Peak hours obviously begin midday when the sun is highest in the sky. During these hours wearing sunscreen and taking precautions against UV exposure are critical.

Fabric Types and Sunscreen Breakdown

Fabrics like polyester and wool have a higher UPF rating whereas fabrics like cotton and linen have a significantly lower UPF rating. The UPF for polyester, for example, is generally 30 or greater. Brands like Patagonia and Outdoor Research have created synthetic fabrics that have a higher UPF while still being lightweight and breathable.

We all should know by now that wearing sunscreen is key to preventing severe burns and reducing skin cancer risk. What else should we know about sunscreen? Chemicals used in certain sunscreens are harmful to reefs and the biodiversity of our oceans. So if you’re visiting coastal regions or islands keep in mind you should purchase reef-safe sunscreen. Some places like Hawaii and the U.S. Virgin Islands have banned the sale of sunscreen containing Oxybenzone and Octinoxate. Sunscreen made with minerals like zinc and titanium can be harmful to reefs as well. So if you are using mineral sunscreen near the ocean make sure the label explicitly states “micro-sized.”

Adventure Time

So where does that leave us in our quest for the perfect adventure day? Remember the clothes you wear make a difference. Sunscreen should always be worn on your face and neck. The closer you are to the sun (i.e. the higher the altitude) the greater the exposure. Hydration is paramount, and when its super hot think about packing some supplemental electrolytes. So grab your reef-safe sunscreen and brightest sun shirt—lets get outside this spring and summer and make some adventures happen!

By Calindra Revier, Content Writer and Media,

Additional links:

Patagonia Sol Patrol Long Sleeve Shirt Men’s

Patagonia Sun Stretch Long Sleeve Shirt Women’s