Everything difficult about sunscreen comes from the fact that it is a film on skin. Films need to be applied in a quantity nobody applies, they are removed by water, sweat and rubbing, they migrate, and there is no way to tell when they have gone.
A garment has none of these problems. It arrives at a known protection level, it does not need to be applied in any particular quantity, it does not wash off in the sea, it does not run into your eyes, and you can see whether you are wearing it. That is a very large set of advantages, and it is why every conditions file on this site reaches the same conclusion: put fabric between yourself and the sun wherever it is practical, and reserve the film for what fabric cannot cover.
What UPF means
Ultraviolet protection factor is the textile equivalent concept to the sun protection factor: a ratio describing how much ultraviolet the fabric transmits. It is determined by measuring transmission through the material.
The standards that matter are AS/NZS 4399, the Australian and New Zealand standard for sun protective clothing, which is the origin of most modern practice in this area, and EN 13758, which covers the solar ultraviolet protective properties of apparel textiles in Europe. A garment sold with a rating has been assessed against a method rather than described by a marketing department.
UPF 50+
What it certifies
That the fabric was assessed under a recognised textile ultraviolet protection standard and achieved the top rated category, meaning it transmits a very small proportion of ultraviolet. AS/NZS 4399 is the long established Australian and New Zealand standard, and EN 13758 covers solar ultraviolet protective properties of apparel textiles in Europe.
What it does not
It rates the fabric, not the garment as worn. It does not tell you about coverage, so a rated vest still leaves your neck, hands and face exposed. And ratings are generally determined on the fabric in a defined state, so wetting, stretching and long term wear may change the real performance of some materials.
What changes the protection of a fabric
Weave density
The most important variable. A tight weave transmits less ultraviolet than a loose one. Hold a fabric up to the light: if you can see a lot of light through the gaps, ultraviolet is going through the same gaps.
Colour
Darker and more saturated colours generally absorb more ultraviolet than pale ones of the same construction. This runs against the instinct to wear white in the heat, and it is one of several reasons dark loose clothing is traditional in hot sunny regions.
Fibre type
Different fibres have different intrinsic ultraviolet absorption, and many technical fabrics include ultraviolet absorbing treatments. Untreated natural fibres vary considerably.
Wetting
Important for anyone reading this site. Some fabrics, notably lightweight cotton, transmit substantially more ultraviolet when wet, because water fills the spaces between fibres and reduces scattering. Purpose made swim and surf fabrics are designed with this in mind. A wet cotton t-shirt is not a reliable substitute for a rash vest.
Stretch
Stretching opens the weave. A garment stretched tight over the body transmits more than the same fabric relaxed, which matters for close fitting sportswear.
Wear and age
Fabrics thin with use and washing, and treatments can diminish. A ten year old rash vest is not necessarily what it was.
Coverage is a separate question from rating
A rating tells you about the material. It says nothing about how much of you is covered. In practice, coverage is where most of the real protection comes from, and the sites that get missed are consistent across every activity on this site: the neck above a collar, the hands beyond a cuff, the face, the ears, the scalp and the tops of the feet. Our note on the scalp, ears and lips covers those.
The practical wardrobe, by activity
- Swimming and snorkelling: a long sleeved rash vest removes the largest and most vulnerable area, the back, from the problem entirely. See snorkelling and diving.
- Surfing: a vest or a suit, because the board removes any film from the chest in minutes. See surfing.
- Cycling and running: light sleeves, which also cool by evaporation. See road cycling.
- Hill walking: a collared or long sleeved shirt, because rucksack straps abrade any film across the shoulders. See hill walking.
- Snow: a buff that stays up, and a helmet that covers, because reflection comes from below. See ski touring.
- Outdoor work: long sleeves and a brim or neck flap, which require no decisions during a shift. See outdoor work.
- Everywhere: a wide brimmed hat, which protects the four sites hardest to keep a film on.
Hats deserve their own paragraph
A peaked cap shades the eyes, the forehead and part of the nose, and leaves the ears and the back of the neck fully exposed. Those two sites are among the most consistently burnt in every outdoor activity. A wide brim, or a peak with a legionnaire flap, covers all of them. If you change one item of kit after reading this site, change the hat.
The economics run the other way
Sunscreen is a consumable you underuse partly because it costs money. A rash vest is a one off purchase that removes an area from the consumption problem for years. For a family, the arithmetic is stark: covering children with fabric is cheaper, more reliable and far less contested than reapplying to a moving target.
Washing, wear and the life of a garment
Fabric protection is durable but not permanent. Three things change it over time.
Thinning. Repeated washing and wear thin a fabric and open the weave. A rash vest that has done five seasons of surf, sand and salt is not the fabric it was.
Stretching. Garments that have been stretched out of shape sit differently and transmit differently, particularly close fitting sportswear.
Treatments. Where a fabric's rating depends in part on an applied ultraviolet absorber, that treatment can diminish over the life of the garment. Manufacturers who use them generally say so.
Interestingly, ordinary wetting is a bigger short term effect than any of these for many fabrics, which is why the swim and surf specific materials exist. A garment you use in the water should be one designed for the water.
Judging an unrated garment
Most clothes have no rating, so a rough method is useful. Hold the fabric up to a bright light and look through it. If you can see a lot of light through the weave, ultraviolet is going through the same gaps. Then consider colour, since darker and more saturated fabrics generally absorb more than pale ones of the same construction, and consider whether the garment will be wet or stretched in use.
That is a crude test and we would not pretend otherwise. It is enough to distinguish a loose pale summer shirt from a dense technical top, which is the distinction that matters most in practice.
What is not verifiable
We do not test fabrics, name garments or rate brands. We cannot tell you the rating of an unrated garment, and neither can you: a t-shirt with no rating has an unknown ultraviolet protection factor, which may be adequate or may not. That is a real limitation of using ordinary clothing, and it is the argument for buying something rated if the activity is demanding.
The one line version
Fabric is the only sun protection that does not wear off. Use it for everything it can cover, and spend your sunscreen on the rest.