what’s the deal with upf shirts?

As a Celt, I've got very sun-sensitive skin. I've gotten second-degree sunburns (blisters, plasma oozing through the skin for days afterwards) at elevation before there were good, moderately water/sweat-proof sunscreens.

I've never gotten a sunburn or even any detectable sun exposure through any garment, SPF-rated or not.

The deal with SPF-rated shirt, IME, is that ALL shirts are SPF-plenty. Like all vegetables are "cholesterol-free".

Yeah, I am skeptical about spf shirts as well.

My main question is why nylon button ups aren't breathable but polyester base layers are breathable, even though they have the same spf rating. I'm assuming a high spf ratings is due to a very tight fabric that doesn't let sun in.

Fiber thickness and density of weave?

Some UPF shirts, at least the ones I've been getting, have zinc or titanium oxides in the fibers that they are woven from, which is what gives them a higher UPF rating (not the density of weave). Since UVB causes sunburn but UVA does not, maybe it's possible that regular clothing blocks UVB but not UVA (as does glass, which is why you won't get burned even if the sun is shining in your car window). UVA causes not sunburn but deeper damage, and is thought to lead more to skin cancers.

I am not a "physical chemistry" guy, but poking around shows that nylon just does not stand up to UV very well.

It degrades quicker than other synthetics, cracking and getting brittle. So my guess is that to make a shirt, you have to "over engineer" it with a tighter and heavier weave.

Also, it does not hold dye very well, which means it is difficult to "add in" stuff that could further absorb UVA and UVB, so making it thicker and tighter is the direction you have to go.

I think the woven nylon shirt has plenty of SPF too; they just haven't paid to test it or didn't think it was important for marketing to list SPF.
As to breathability, a knit shirt is going to be more breathable than a tightly woven shirt.

I think the companies listed build the shirt first, then drag the UPF rating in as an added benefit. IMHO, the nylon button down shirts are designed more with durability in mind. All my button down shirts are far more breathable than a windshirt, but nothing like a wicking base layer.

Consider polyester dress shirts for outdoor use too.

There are companies making sun protection clothing and their designs center on full coverage features like tall collars and neck opening gussets— and vents to make up for the hotter full coverage designs. The fabric seems to be rather ordinary outdoor stuff. I havent seen anything with titanium oxide additives, which sounds interesting.

A UPF rating of 30 means that with 30 units of exposure, 1 unit gets through. That comes out to 97% coverage.

And of course there is a Wiki on this:
http://en.m.wikipedia.org/wiki/Sun_protective_clothing

"The deal with SPF-rated shirt, IME, is that ALL shirts are SPF-plenty."
Wishful thinking. Having lived on the Gulf Coast as a kid, I've seen plenty of people sunburned through shirts, particularly thin light-colored ones. Was still surprised just now when I googled, and found this quote.

"Think that T-shirt protects your kid from UV rays? Think again. A white T-shirt has an SPF of about 7, but once it gets wet, SPF drops down to about 3, according to the Skin Cancer Foundation."

Edit: Looking around out of curiosity, and found this, but I'm not curious enough to follow the link and start looking up clothing items…

Euh, the term is UPF. SPF is only used for sun tan lotion.

I'm glad that DK mentioned the difference between UVA and UVB. You don't have to get a sunburn to damage your skin. I had to have a cancerous melanoma sliced out of my cheek and so I've become a bit soap boxy on this subject. On the subject of car windows blocking out rays: There's an interesting photo on the internet of a long haul driver's face. The left, window facing side is completely saggy and sun spotted. The right side is much more normal. The point is that all car glass doesn't protect you from potentially damaging rays, even if you don't burn. You can look up your car model and find out about the kind of glass in your windows.

Hiking at elevation really increases the intensity of the sun's rays. And no, cotton doesn't do a good job at blocking sun rays. This, according to the dermatologist who sliced me up. He's not in the pockets of the nylon-medical-industrial complex. I think that it's worth doing some research and getting a good sun shirt and hat.

http://www.coolibar.com/mobile/custserv/custserv.jsp?pageName=suntect

Here is a listing of the various fabrics used by one company.

Those of us that have had skin cancers removed tend to look a little more deeply into the subject of sun protection…

Isn't the UPF rating for the fabric? Doesn't account for how well the shirt covers your neck or arms or anything?

I don't think anyone will wear their shirt enough hours for it to be degraded by UV, so nylon is fine. If you have a tent out for an entire summer in the sun (or a boat cover or awning or whatever) then UV resistance is important so nylon not so good a choice.

A mesh shirt or really thin fabric you can see through won't offer much protection, but a typical shirt for hiking is probably good enough.

Even a UPF rating of 7 would be fairly effective. A lot of the time I'm in the shade – trees, or resting. 15 minutes of exposure is a good thing, so UPF 7 would be 2 about hours in the sun. And 30 minutes or an hour of exposure isn't that bad. Long days at altitude with no shade, Sierras for example, then UPF 30 is good. Or if there's a lot of snow reflecting the light.

"Think that T-shirt protects your kid from UV rays? Think again. A white T-shirt has an SPF of about 7, but once it gets wet, SPF drops down to about 3, according to the Skin Cancer Foundation."

That statement, at least without any qualification, is distinctly at odds with the table shown below it in Owen's post. I take it with a huge grain of salt, like most everything that particular Foundation says. If that statement were true, we wouldn't have terms like "tan lines," "farmer's tan," or "redneck" in our language.

Here's another one from their website:

"Who Should Use Sunscreen?

Anyone over the age of six months should use a sunscreen daily. Even those who work inside are exposed to ultraviolet radiation for brief periods throughout the day, especially if they work near windows, which generally filter out UVB but not UVA rays."

Source: http://www.skincancer.org/prevention/sun-protection/sunscreen/sunscreens-explained

They actually say that *everyone* should wear sunscreen *every day* even if they are indoors all day because–horrors–some buildings have windows. That borders on asinine and leads me to almost dismiss everything they say. I give them the same deference I give to the nutrition "experts" who, after two decades of telling us to get the fat out of our diet, are now having to watch the health disaster that is 20 years of insulin spikes. If I were a betting man, I'd wager that slathering 3 oz (the Foundation's approximate recommendation) of sunscreen on your skin 365 days per year will ruin your health a lot faster than the moderate amount of sun you'll get just by not living underground.

zombie thread, but it should be added.

The chemistry of Polyester results in strong absorption in the UV spectrum.  Nylon and other fibers do not exhibit this.

Of course, thickness and density of weave are critically important as well.