How to Understand Sun Protective Clothing

As the summer season kicks off we get a lot of people looking for sun protective clothing, which is great! Unfortunately, we can’t help but notice that there is sometimes a fundamental misunderstanding about how sun protective clothing works, what UPF means, and how to put it all in context. That’s what this post will attempt to clarify.

As the sun’s rays get stronger and people spend more time out on the water or vacation to more equatorial locations, the need for adequate sun protection is incredibly important. Exposing your skin to UV rays is not only damaging and unpleasant in the short term, but also carries a host of long-term complications.  To mitigate this, you need to wear sunscreen or appropriate clothing. Clothing is sometimes advertised with a UPF rating. Let’s break that down.

What is UPF?

UPF, or Ultraviolet Protection Factor, is a direct measure of the ability of clothing to block ultraviolet light. Unlike SPF, it does not involve any measure of exposure time. It is simply an expression of the ratio of UV light that passes through the fabric. For example, a UPF 40 garment will allow around 1 out of 40 units of UV rays through the fabric. That’s 97.5% blocked. A UPF 50 garment will allow 1 out of 50 units of UVB, or 98% blocked.

How does UPF work?

It’s pretty simple. The denser the weave, the higher the thread count, the more protective the garment is because it lets less light through. Surprise! It’s got less to do with the thickness of the fabric, and much more to do with the weave density and fabric type.

To further demonstrate how thicker doesn’t necessarily mean better, take a comparison of the Patagonia Capilene Thermal Weight baselayer, and the Patagonia Capilene Daily garments. The Thermal Weight Capilene is thicker, almost like fleece, but its loose surface weave means that I can see my hand through it. Though it’s not always a direct relationship, it should be pretty obvious that a garment I can easily see the color of my skin through is probably not going to be as effective. Conversely, the Capilene Daily has a much higher thread count on the surface fabric, making it a denser weave, which gives it a great UPF 50 rating. It’s thinner but that doesn’t matter as much, as we’ve shown.

Garment color can play a role as well. Darker colors are more effective at blocking UV rays for the same reason that window tinting is effective. However, darker colors also absorb more heat which may make it less desirable for hot environments.

Fabric type can also determine effectiveness. Synthetic fabrics like polyester and nylon are far more effective than cotton or hemp. As a point of reference, a white cotton T shirt has about a UPF 5, even worse when the cotton gets wet.

This garment doesn’t have a UPF rating, does that mean it’s not protective?

No, not necessarily.

The concept of the UPF system as we know it didn’t come into being until the mid 1990s. Quite obviously, people have been wearing sun protective clothing for thousands of years because it’s been understood that clothing protects your skin. They also understood that a denser weave was better. It is of no surprise that many desert-dwelling peoples use long, loose fitting garments to cover as much skin as possible and to keep cool.

The FTC has oversight over UPF standards. If a manufacturer has an interest in advertising their product as sun protective, they will undergo testing and certification on the product. So, it’s possible that a garment is effective, but the manufacturer may not have chosen to undergo testing. Use your best judgment, and if you’re still on the fence then there are thousands of options from hundreds of manufacturers out there who have done the testing.

How much UPF do I need?

This varies depending on what you’re doing and where you’re going, like so much of outdoor clothing and equipment.

Obviously, if you have fair skin you want a higher UPF rating. If you’re going to a place with harsher sun exposure such as in the desert, at higher altitude, to equatorial latitudes, or on the water, then you’ll want a higher UPF rating.

Typically, UPF rated clothing will range from about UPF 15 to UPF 50. General summer wear is usually around UPF 15 or 20. I would look for at least UPF 30. Speaking for myself, I prefer UPF 40 or 50 since I am pale and really, really don’t want to repeat the 360 degree lobster-red sunburn I received on a Lake Erie fishing trip on a sunny day.

The General Takeaway

Use your best judgment given your skin and your plans, and try to seek out higher UPF clothing with a long, loose fit. Wear a wide-brimmed hat or a buff, or seek out a light sun-protective hoody. If it’s a sheer cloth or a mesh bug overshirt, it’s pretty clearly not going to do much for you. Don’t forget your hands, either. Several manufacturers make a light sun-glove. Always use and liberally re-apply sunscreen to exposed areas. Wear sunglasses! Your eyes can get sunburned too, and it’s about as unpleasant as it sounds.

Don’t underestimate the sun, and you’ll have a much better time out and about this summer!