# My new shirt has an SPF of 30+!?? **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2000, 5:08pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580 "2000-07-14T17:08:11Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Powers106](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@Powers106](https://boards.straightdope.com/u/Powers106)\ **Post date:** [July 14, 2000, 5:08pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/1 "2000-07-14T17:08:11Z")
I bought a shirt at one of these outdoor clothing stores and a little tag on it proudly announces that it has an SPF of 30+ and blocks out ultraviolet rays or something. This is written as if a special treatment has been sprayed on the fabric and that it is really special. I think this is just a silly marketing ploy, virtually any shirt that covers your skin is going to be 30+, but, hey, you never know. Is my new shirt special? ---
**Author:** ![Quadzilla](https://avatars.discourse-cdn.com/v4/letter/q/a4c791/32.png) [@Quadzilla](https://boards.straightdope.com/u/Quadzilla)\ **Post date:** [July 14, 2000, 6:38pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/2 "2000-07-14T18:38:59Z")
The SPF may not be for you; it may be a protection factor for the shirt itself to keep it from fading in the sun. Dunno, just a WAG. ---
**Author:** ![redtail23](https://avatars.discourse-cdn.com/v4/letter/r/3e96dc/32.png) [@redtail23](https://boards.straightdope.com/u/redtail23)\ **Post date:** [July 14, 2000, 6:56pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/3 "2000-07-14T18:56:39Z")
Yep, it’s for real. Studies done recently (last 5 years or so IIRC) show that most summer clothing offers NO significant protection from the sun. This is highly critical to skin-cancer patients and fairly important to extremely fair-skinned people. A couple of companies (one founded by skin-cancer survivors who couldn’t find sun-blocking clothing) have started producing SPF/UV blocking clothing. [http://www.skincancer.org/sunsafe/](http://www.skincancer.org/sunsafe/) [http://www.solumbra.com/home.htm](http://www.solumbra.com/home.htm) [http://www.sharksuit.com/index.html](http://www.sharksuit.com/index.html) [http://www.vipimage.com/alpha100+/index.htm](http://www.vipimage.com/alpha100+/index.htm) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 14, 2000, 9:06pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/4 "2000-07-14T21:06:59Z")
OK, redtail23, I’m confused. In the summer, I just wear plain, ordinary t-shirts, and I never put on sunscreen under clothes, and yet I never tan or burn in areas covered by clothing (I do burn in those areas if unprotected). What’s happening there? ---
**Author:** ![tcburnett](https://avatars.discourse-cdn.com/v4/letter/t/c5a1d2/32.png) [@tcburnett](https://boards.straightdope.com/u/tcburnett)\ **Post date:** [July 14, 2000, 9:39pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/5 "2000-07-14T21:39:32Z")
> [@](#): > > \*Originally posted by Powers106 \* > \*\*I think this is just a silly marketing ploy, virtually any shirt that covers your skin is going to be 30+, but, hey, you never know. Is my new shirt special? \*\* Anything which prevents direct sunlight on your skin has an SPF. I wear a .5 mil neoprene wetsuit when I dive. The SPF is pretty high at the surface and close to infinity underwater. Hey, if you like the shirt, you got something extra! If you BOUGHT it for the SPF, the marketing ploy works. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 14, 2000, 10:01pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/6 "2000-07-14T22:01:28Z")
I have also seen several reports that say ordinary clothing offers very little protection and it clashes with my own intuition. But I have learnt not to trust intuition and “common sense”… I would be interested in knowing more about this. ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [July 14, 2000, 10:22pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/7 "2000-07-14T22:22:47Z")
“Ordinary clothing” is a little broad. A very coarse-weave garment, such as some sweaters, will obviously not have a high SPF- sunlight comes in through the weave. A tight-knit shirt will be much better. Individual strands of thread have a very high SPF, but cloth isn’t a solid thread, it’s a weave of threads, possibly separated by some space. Hold your t-shirt up to the sun and see if you can see any light through it. Don’t stretch it, let it hang the way it hangs on you. Is it opaque, or can you see some light shining through? Of course, passing visible light isn’t the same as passing UV, but for things like clothing it’s not a terrible estimate. Arjuna34 ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [July 14, 2000, 11:31pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/8 "2000-07-14T23:31:39Z")
Whats it made of Arj??? Depends on whether its synthetic fabric or not. SPF stuff would wash off quickly. ---
**Author:** ![Tapioca\_Dextrin](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@Tapioca\_Dextrin](https://boards.straightdope.com/u/Tapioca_Dextrin)\ **Post date:** [July 15, 2000, 12:50am UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/9 "2000-07-15T00:50:14Z")
Lycra provides really great SPF. You should see what a cyclist looks like after a few weeks riding in the sun. In Australia, where skin cancer is a real threat, lycra body suits (complete with hoods!) for kids are getting really popular - the kids can play all day on the beach all day and still come back completely untanned. ---
**Author:** ![Wood\_Thrush](https://avatars.discourse-cdn.com/v4/letter/w/b38774/32.png) [@Wood\_Thrush](https://boards.straightdope.com/u/Wood_Thrush)\ **Post date:** [July 15, 2000, 2:22am UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/10 "2000-07-15T02:22:48Z")
> [@](#): > > \*Originally posted by Arjuna34 \* > **Hold your t-shirt up to the sun and see if you can see any light through it. Don’t stretch it, let it hang the way it hangs on you. Is it opaque, or can you see some light shining through?** That is _not_ a good idea. _Never, ever_ look at the sun under _any_ circumstances! Perhaps **Arjuna34** forgot that kindergarten lesson. 😃 Before we tackle this, we need to know what UV radiation is. You’ll get the idea from the following quote, but read all of the article for more information. From “[Shedding Light on UV Test Equipment](http://www.restassured.com/UV_report.html)” by Les Davis: > [@](#): > > **Which type ot UV does what?** > > A glance at the electromagnetic radiation spectrum (see [Figure 1](http://www.restassured.com/images/fig1.gif) ) shows that UV is commonly divided into three ranges: > > **1. Short wave (UV-C):** Extending from 180nm to 280nm, this wavelength is used for such applications as UV sterilization, chromatography, laboratory analysis, mineralogy, erasable programmable read-only-memory (EPROM) erasing, and photochemical reactions. Protective clothing and eyewear are needed with UV-C. Although high-energy UV-C has little penetrating power, it can cause severe eye and skin bums to people without protection. > > **2. Medium wave (UV-B):** Occupying the 280nm to 320nm region, UV-B is used in DNA (deoxyribonucleic acid) research, in artificial sunlamps for cosmetic tanning, for therapeutic purposes, and for vitamin production. With high-penetration power but less energy, UV-B can still seriously burn unprotected eyes and skin. > > **3. Long wave (UV-A):** This low-energy wavelength, which covers the 320nm to 400nm range and is also known as black light or Wood’s light, is the most useful for UV testing. UV-A is ideal for NDT and QC inspection, leak testing, UV curing, general fluorescence analysis, medical diagnosis, counterfeit check and currency detection, invisible signature verification, and invisible UV marking and displays. Long-wave UV requires no protective clothing. However, the use of UV-blocking spectacles or goggles is recommended. They make traces more apparent by increasing fluorescent contrast and eliminating blue-haze interference while they also protect eyes from irritation due to repeated UV exposure. And finally, an answer to the OP. From [U.S. News: Sunscreens vs. sun-protective clothing (8/9/99)](http://www.usnews.com/usnews/issue/990809/nycu/clothes.htm): > [@](#): > > **Inflated figures.** UV-protection numbers used by some vendors should not be taken at face value, however. No standardized technique exists in the United States for measuring how well fabric blocks sunlight. Australia has a [standard](http://www.arpansa.gov.au/is_protct.htm#Standard) that applies to new, dry material, and a voluntary one could be in place in this country by the end of the year. Clothing that is wet or has been washed repeatedly, however, could be much less effective. > > Besides, ordinary clothing is usually enough–if a few rules are heeded. Since the goal is to block the sun, a tight weave is vital; the more light that can be seen through the fabric, the worse the protection. Darker colors generally are better than light ones, because darker dyes absorb more UV rays. But dark clothes are hotter, so choose garments that are lightweight and loose fitting. “I wear a lot of cotton knits, with sleeves I can push up or roll up,” says Hatch. “If I wear a sleeveless dress, I usually have a long-sleeved blouse I can wear with it when I’m out in the sun. I’m a realist. I tell people: Find things you normally wear in a style you can live with.” ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [July 15, 2000, 2:09pm UTC](https://boards.straightdope.com/t/my-new-shirt-has-an-spf-of-30/25580/11 "2000-07-15T14:09:37Z")
I forgot if it was synthetic fabric that has no SPF protection when its wet or natural fabric.