Practical guide·Sun protection
UPF 50+: what this rating really means and why it changes everything
A fabric's ability to block UV rays cannot be seen. It has to be measured.
Most people judge a garment's sun protection by eye. Thick fabric, a dark colour, and we assume we are perfectly protected. Yet a fabric's ability to block UV rays cannot be seen. It has to be measured.
The rating used for that measurement is called UPF, or Ultraviolet Protection Factor. Without it, there is no way to know how much UV radiation actually reaches the skin beneath a garment.
Let's take a closer look at what this rating means, how it is calculated, what the standards guarantee and why UPF 50+ represents the only reliable guarantee of sun protection.
What is UPF?
UPF stands for Ultraviolet Protection Factor. It is the rating that measures a fabric's ability to reduce the amount of UV radiation that passes through the textile and reaches the skin.
The principle is simple: the higher the rating, the greater the protection.
A fabric rated UPF 50+ means that it takes around 50 times more UV exposure to cause erythema on protected skin than on unprotected skin.
This measurement is standardised and assessed in the laboratory according to EN 13758-1. It takes both UVA and UVB into account, weighted according to their ability to cause erythema.
They penetrate more deeply into the skin and are notably involved in photoageing. They largely pass through glass and remain present all year round.
They are the main cause of sunburn and play an important role in skin DNA damage. Their intensity varies more with the season, the time of day and altitude.
A fabric's UPF therefore takes both components of UV radiation into account.
What UPF 50+ really means
You have probably already read this statement: "UPF 50+ blocks 98% of UV rays." It is very widespread, but it simplifies reality.
UPF cannot be reduced to a simple percentage of rays blocked. It is based on a measurement weighted by the biological effect of UV radiation on the skin, especially its ability to cause erythema. In other words, UPF tells you the real level of protection the fabric provides against the risk of sunburn on covered areas.
A garment certified UPF 50+ provides a very high level of textile protection on the areas it covers. This does not remove the need for overall sun protection: a hat, sunglasses, seeking shade, limiting exposure when UV levels are high, and sunscreen on uncovered areas.
UPF 50+ is the highest anti-UV certification level under the European standard EN 13758-1. A UV-protective garment certified UPF 50+ effectively protects your skin against possible burns and damage.
UPF protection levels: the official table
As a guide, the following levels are often distinguished:
| UPF rating | Recognised protection |
|---|---|
| UPF 15–24 | Good |
| UPF 25–39 | Very good |
| UPF 40–50 | Excellent |
| UPF 50+ | Maximum under the standard |
Please note: below UPF 40, a garment cannot legally be called a "UV-protective garment" in Europe. To claim compliance with EN 13758-2, the fabric must in particular have a UPF above 40 and an average UVA transmission below 5%.
The classic cotton T-shirt: the reality few people know
Here is a figure that surprises almost everyone.
In other words, being covered does not necessarily mean being well protected. And when that T-shirt gets wet, its UPF drops even further.
Good to know
A certified UPF 50+ garment is tested dry, as specified by the standard, but Ker Sun has put a process in place through which we also test our Ker Sun swimwear and sportswear when wet in order to guarantee maximum protection even when wet.
What determines a fabric's level of protection
Several factors influence a fabric's ability to limit the passage of UV radiation.
The density of the weave or knit plays a major role: the tighter the textile, the higher the protection is generally likely to be.
The fibre composition also matters. With a comparable structure, certain synthetic textiles such as polyester or polyamide can offer better protection than lighter or more open fibres.
Colour can also influence protection: dark or rich shades often protect better than very light shades. But on a garment certified UPF 50+, it is first and foremost the fabric's overall design that matters, not just its colour.
Lastly, some fabrics reach their level of protection through their construction alone, while others rely partly on added treatments. Protection achieved mainly through the structure of the fabric may be more stable over time, but wear, care, stretching and moisture remain important factors.
EN 13758: what the standard guarantees exactly
In Europe, two standards govern textile UV protection.
EN 13758-1 defines the test method used to assess the UV-protective properties of fabrics intended for clothing.
EN 13758-2 governs the classification and labelling of garments claiming that protection. In particular, it sets minimum fabric performance requirements as well as garment coverage requirements.
For example, for the upper body, the standard targets coverage from the base of the neck down to the hips, with sleeves extending to three-quarters of the arm. For the lower body, the protected area runs from the waist to below the kneecap.
This twofold logic is important: a high-performance fabric is not enough on its own if the garment's cut leaves too much skin exposed.
PPE (personal protective equipment) and CE marking: why it matters
This is the point that most consumers are unaware of, and yet it changes everything.
When a garment is marketed as protective equipment against a UV-related risk, the European regulatory framework for PPE comes into play. Regulation (EU) 2016/425 governs personal protective equipment placed on the European market.
Within that framework, the CE marking and the EU declaration of conformity are not decorative elements: they embody the manufacturer's commitment to regulatory compliance.
Ker Sun sun-protective garments and accessories are classified as Category I PPE, the category covering known and foreseeable risks.
Good to know
A garment that claims UV protection without CE marking is not PPE (personal protective equipment) that complies with European law. The CE marking is not a style logo; it is a legal attestation. All Ker Sun products are certified UPF 50+ and carry the CE marking. 100% of the range complies with PPE Regulation 2016/425.
SPF 50 and UPF 50+: the same protection?
The question comes up often: if my sunscreen is SPF 50, am I as well protected as I would be with a UPF 50+ garment?
On paper, the two ratings express a similar idea: they indicate to what extent protection delays the appearance of erythema. But in practice, SPF and UPF do not behave in the same way.
SPF 50 sunscreen: SPF is calculated using a specific reference dose of 2 mg of product per cm² of skin. In real-life conditions, that dose is rarely achieved. When the amount applied is insufficient, or reapplication is forgotten after swimming or perspiring, the actual protection can be much lower than the level shown on the bottle.
UPF 50+ garment
A garment certified UPF 50+ works differently: its protection comes from the textile itself. It does not depend on any application or reapplication on covered areas. That is what makes it particularly reliable in everyday life.
In practice, SPF 50 and UPF 50+ are only really comparable in the laboratory. In real life, certified UV-protective clothing provides more consistent protection, precisely because it does not depend on user behaviour.
For optimal sun protection, it is still recommended to combine UV-protective clothing with a hat, sunglasses and SPF 50 sunscreen on exposed areas.
In summary: a UPF 50+ garment, three levels of guarantee
What a garment certified UPF 50+ really guarantees is the combination of three levels:
EN 13758-1 · Fabric measurement
UPF measures the fabric's ability to delay erythema, calculated by integrating the real biological harmfulness of UV radiation.
EN 13758-2 · Classification & labelling
The standard imposes the minimum level (UPF 40, UVA transmission < 5%), coverage requirements, and the mandatory warnings on the label.
CE · PPE Regulation 2016/425
CE certification attests compliance with PPE Regulation 2016/425: the garment is officially a personal protective device, assessed and declared compliant with European health and safety requirements.
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