Quick answer
Yes — clothing is one of the most reliable forms of sun protection, because unlike sunscreen it doesn't rub off or need reapplying. But not all clothing protects equally: a thin white cotton t-shirt sits at roughly UPF 5–7, while a garment certified UPF 50+ blocks around 98% of UV. Weave density, colour, fit and whether the fabric is wet matter more than the fibre name on the label.
Every summer the same question comes up in the shop and in our inbox: my toddler won't keep sunscreen on, is a long-sleeve top enough? It's a fair question, and the honest answer has some nuance in it. Clothing is genuinely excellent sun protection — dermatologists rank it above sunscreen for small children, especially babies under six months, where the American Academy of Dermatology recommends shade and covering up rather than sunscreen at all. But the difference between a good sun shirt and a thin summer tee is bigger than most parents expect.
What UPF actually measures
UPF stands for Ultraviolet Protection Factor. It's the textile equivalent of SPF, with one important difference: SPF on a sunscreen bottle measures UVB only, while UPF accounts for both UVA and UVB radiation passing through the fabric.
The maths is simple. A UPF 50 fabric lets through 1/50th — about 2% — of the UV that hits it, blocking roughly 98%. UPF 30–49 is considered very good protection; UPF 50+ is the highest rating awarded and, in most schemes, the top of the scale. Anything under UPF 15 generally isn't allowed to be labelled as sun-protective at all.
In Europe there's a formal standard behind the claim: EN 13758. Part 1 sets out the laboratory test method (measuring UV transmittance from 290–400 nm), and Part 2 covers classification and marking. To carry the EN 13758-2 pictogram, a garment must reach UPF 40+, keep average UVA transmission under 5%, and meet design requirements — meaning coverage counts, not just the swatch of fabric. That last point is often missed: a certified crop top doesn't protect the shoulders it doesn't cover.
Why a normal t-shirt isn't as protective as it feels
A standard thin white cotton t-shirt offers roughly UPF 5–7. That means around 15–20% of UV still reaches the skin underneath — enough to burn a fair-skinned child on a strong summer day at the beach.
Four things move the number, and they're all visible to you without a lab:
- Weave density. Hold the fabric up to a window. If you can see daylight clearly through the weave, UV goes through it too. Densely woven or knitted cloth blocks more.
- Colour. Deeper and more saturated colours absorb more UV. Dyeing a basic cotton shirt a dark or vivid shade can lift it into the UPF 10–15 range — better, but still far from 50.
- Fit. Stretched fabric opens up its own weave. A shirt pulled tight across a child's back protects measurably less than the same shirt worn loose. This is one of the quiet advantages of an oversized cut.
- Wetness. This is the big one. Water fills the air gaps between fibres and reduces UV scattering. A wet cotton t-shirt can drop to around UPF 3 — letting more than 30% of UV straight through. A child playing in a soaked cotton tee in a paddling pool is close to unprotected.
How everyday fabrics compare
| Garment | Approx. UPF dry | What changes it |
|---|---|---|
| Thin white cotton tee | ~5–7 | Drops to ~3 when wet or stretched |
| Dark or saturated cotton tee | ~10–15 | Colour helps; weave still lets UV through |
| Loose-weave linen shirt | Low – varies widely | Very breathable, but open weave; layer over a vest |
| Densely woven cotton twill / denim | High | Excellent coverage; warmth is the trade-off |
| Certified UPF 50+ sun shirt | 50+ | Holds its rating when wet if properly constructed |
We want to be straight with you here: our own clothes are made for everyday wear, not tested and certified to EN 13758. They're densely woven GOTS-certified organic cotton in deep, saturated colours with a generous oversized cut — all three of which help — but if your child is going to spend a full day in and out of water in strong sun, a dedicated certified UPF 50+ swim top is the right tool for that job. Good sun protection is a system, not a single garment.
Building a sun-safe outfit that a child will actually wear
The best sun-protective garment is the one that stays on. A few things we've found work:
- Go loose, not tight. A roomy long-sleeve top in a light, breathable weave feels cooler than a snug short-sleeve one, because air moves underneath it. It also keeps the weave relaxed and more protective.
- Cover the hard-to-reach places. The back of the neck, the tops of the ears and the tops of the feet are the spots parents most often miss with sunscreen. A brimmed hat that shades the neck solves two of them at once.
- Long trousers beat shorts plus sunscreen for a full day outdoors — one less thing to reapply on a wriggling three-year-old. Loose linen-cotton or lightweight denim works.
- Bring a dry change. Since wet fabric loses most of its protection, swapping a soaked top for a dry one after the paddling pool matters more than it sounds.
- Use the clock. Dermatologists consistently point to the 10:00–16:00 window as the highest-UV part of the day. Shifting the park trip to the morning does more than any fabric can.
Does UPF wash out?
It depends on how the protection was built in. Where UPF comes from the fabric itself — a dense weave, a deep dye, a heavier yarn — it lasts as long as the garment does. Where it comes from an applied UV-absorbing finish, that treatment can gradually diminish over many washes.
Two counter-intuitive notes. First, cotton often gets slightly more protective after its first few washes, because the fabric shrinks a little and the weave tightens. Second, protection falls as a garment wears out: thinned, faded, stretched fabric with visible pilling lets more light through than it did new. If you can see daylight through the shoulders of a much-loved hand-me-down, it's doing less than it used to — which is a reasonable moment to move it down the pile to layering duty. Washing gently and drying in the shade keeps both the colour and the coverage for longer.
FAQ
Is a long-sleeve cotton top enough sun protection for a toddler?
For everyday shade-and-sun play in the Netherlands, a densely woven, darker long-sleeve top plus a brimmed hat covers a lot of ground. For a full day at the beach or in strong Mediterranean sun, add sunscreen on exposed skin and consider a certified UPF 50+ top — especially around water.
Can I put sunscreen on a baby under six months?
The American Academy of Dermatology and the FDA advise against routine sunscreen use below six months, because it hasn't been studied in infants that young. Shade, covering clothing and a brimmed hat are the recommended approach; if shade genuinely isn't available, a small amount of mineral sunscreen on the face and backs of the hands is the usual fallback. Ask your consultatiebureau or GP if you're unsure.
Does a dark colour really protect better than white?
Yes — deeper, more saturated dyes absorb more UV, and can roughly double the UPF of an otherwise identical cotton shirt. The trade-off is heat absorption, which is why a loose fit matters: air circulating under the fabric keeps a dark garment comfortable.
Is linen good sun protection?
Linen is wonderfully breathable but often loosely woven, and openness in the weave is exactly what UV travels through. A linen overshirt works best layered over a closer-woven vest or tee rather than worn against bare skin all day.
Do second-hand kids' clothes still protect?
Mostly yes — weave-based protection is durable, and cotton tends to tighten slightly with washing. What to watch for is genuine wear: thinning, heavy fading, pilling or stretched-out fabric. The window test still applies, whatever the garment's history.
How do I know if a garment is genuinely certified?
In Europe, look for the EN 13758-2 pictogram with a stated UPF of 40+. A garment simply described as “UV protective” with no standard referenced is a marketing claim, not a tested rating.
Keep exploring
- Cotton, Linen, or Bamboo? The Best Fabrics for Kids in Summer Heat
- How to Wash and Care for Organic Cotton Kids Clothes
- Dressing Kids with Eczema or Sensory Sensitivities: A Fabric & Fit Guide
- How to Pack Kids' Clothes for Travel: A Sustainable Mix-and-Match Guide
Our own summer pieces are cut oversized and woven densely in GOTS-certified organic cotton — you can see the full range in the shop, or browse pre-loved pieces in Twice Loved.