What does UPF mean on a riding shirt?

The Skin Cancer Foundation describes it that way and gives a plain example: a fabric rated UPF 50 blocks 98 percent of the sun's rays and lets 2 percent, one fiftieth, through.

That is the whole idea behind a riding sun shirt. It is a long-sleeve top in a lightweight, breathable knit, and the UPF number is the one figure on the tag that says something measurable about the sun. As our casual riding tops page puts it, any UPF figure comes from the vendor, so it pays to read the listing instead of assuming.

UPF is about UV getting through cloth and nothing else. It does not tell you how cool, soft or flattering a shirt is. Those come down to the knit and the cut, and we get to them below.

That is the University of Arizona's extension guide to UV-protective clothing labels, which also lists how much UV each band blocks.

The Skin Cancer Foundation keeps it simpler: UPF 30 to 49 is very good protection and UPF 50+ is excellent. The two sources agree where they overlap. A shirt marked UPF 30 sits in the very good band either way.

Two details from the Arizona guide are worth knowing at the rack. First, labels under the recognized standards step up in fives from 15 to 50 and then say 50+, so an oddball figure like 17 or 23 should raise an eyebrow. Second, 50+ may not offer much more than 50, so a shirt marked 50+ is not automatically far ahead of one marked 50.

The University of Arizona guide names two recognized standards: ASTM D6603 in the US (the guide writes it as ASTM 6603-00) and AS/NZS 4399 from Australia and New Zealand. When two garments carry the same UPF under different standards, the guide suggests choosing the one tested to the ASTM standard, because that fabric is laundered 50 times before testing, while the AS/NZS garment is tested as new.

The Skin Cancer Foundation runs its own program. A fabric needs a UPF of 50 to qualify for the foundation's Seal of Recommendation, and it suggests looking for the seal when you shop.

On our own shelves the number is whatever the vendor states. Our casual riding tops page notes that Kerrits states UPF+30 on the Ice Fil Lite Short Sleeve Shirt Solid and on the Equibreeze Print Ice Fil Long Sleeve Shirt, and that Kerrits describes Ice Fil Lite as a featherweight fabric that pulls heat from the skin. That is the brand's description, not a rating of ours. Other brands make their own sun-shirt and cooling-knit tops, and each listing shows what that vendor claims, if anything, so check the fabric note before you compare.

One more honest caveat from the Arizona guide: the FTC monitors these claims in the US, but the guide says it isn't known how much monitoring actually happens. A number on a tag is a starting point, not a guarantee.

The Skin Cancer Foundation lists the factors: densely woven cloth protects better than sheer or loosely woven cloth, dark or bright colors absorb more UV than lighter ones, and loose clothing beats tight clothing because tight fabric can stretch and pull its fibers apart. Wet or stretched fabric loses protection. The foundation's own example is a white T-shirt with a UPF of about 7 that drops to about 3 when it is wet.

The American Cancer Society gives a quick home test: if you can see light through a fabric, UV rays can get through it too. It also says dry fabric is generally more protective than wet, while noting that some lightweight UPF clothing stays protective when wet, which is something the tag or the maker has to tell you.

Wash and wear matter less than you might fear if the shirt was tested to the ASTM standard, since the Arizona guide says that standard launders the fabric 50 times before testing. It is still reasonable to ask how a given shirt's rating was measured, and whether it was tested new or after washing.

The American Cancer Society is blunt that covering up doesn't block all UV rays. It says long-sleeved shirts, long pants and long skirts cover the most skin and are the most protective, and it recommends using as many protective measures as you can. It also notes that sunscreen filters UV rays but doesn't block them fully, and that it belongs on skin your clothing doesn't cover.

That is where sleeve length and neckline come in. The Arizona guide points out that the protection category on a label says nothing about how much skin a garment covers, and recommends choosing garments that cover more than the usual amount. Our casual riding tops page sorts it by season: long sleeves for sun and wind, short sleeves for arena schooling and for layering. A long sleeve with a long neck zip, like the Kerrits Equibreeze Print Ice Fil Long Sleeve Shirt, lets you open the neckline when the sun comes out. Whatever that opens up is skin that needs its own cover.

Keep the claim in proportion, too. The Arizona guide says UPF claims are for sunburn protection and that benefits such as less skin aging or lower skin cancer risk are not claimed, because UPF testing doesn't measure them. For questions about your own skin, ask a doctor or dermatologist.

Here is how one rider describes a cooling sun shirt.

There is a real trade-off underneath. The Skin Cancer Foundation says dense weaves protect better than thin ones, so a heavier, tighter knit can score higher on UPF and still feel warmer to wear. A lighter knit can feel better in the saddle and land lower on the scale. The listing's fabric note and its UPF line answer two different questions, so read both.

Our sources can tell you what UPF means. They can't tell you how a specific knit will feel at your barn in August, so this is a place where rider experience is the best guide.

Our casual riding tops page points to what riders say about Kerrits Ice Fil shirts worn through hot summers in Arizona and Southern California, and it describes sun shirts as schooling tops. If you ride somewhere muggy, look for the same things riders in dry heat mention: a lightweight knit, venting where you sweat, and a fit that isn't tight against the skin. The Skin Cancer Foundation also says loose clothing is better than tight for protection, so a looser cut is a double win.

Not every cooling-knit top is sold as a sun shirt, and not every sun shirt lists a number. Here is the checklist the sources above add up to:

• A UPF figure on the usual steps: 15, 20, 25, 30, 35, 40, 50 or 50+.
• The standard the number came from, ideally the US ASTM standard.
• The fabric note: weight, weave and any cooling or venting details.
• Color and cut: darker or brighter and looser protects better than pale and tight.
• Sleeve length and neckline, since UPF only covers what the shirt covers.
• The vendor's wording. Our casual riding tops page keeps vendor claims attributed to the vendor, and so should you.