Black or White? What Your T-Shirt Is Doing to You on a Hot Day

Next time you’re out on a warm day, take a look around at what people are wearing. On a recent riverside walk in Bovey Tracey — a pleasant 21°C, nothing extreme — it was striking how many dog walkers were in black, either head to toe or just a black top over pale trousers. It’s a small thing, but it got us thinking: does it actually matter?

Turns out, yes — quite a bit, in the right conditions.

The physics in one sentence

Dark fabric absorbs several times more solar energy than light fabric.

That makes you hotter.

Measurements of identical materials in different colours put black at absorbing (and heating you up) around 80–90% of incoming sunlight, against roughly 20–40% for white. Khaki and other mid-tones sit somewhere in between. On a sunny day, surface temperatures on a black T-shirt have been measured at 5–10°C hotter than an identical white one.

But here’s the twist

It’s actually not quite as simple as “black clothes make you hotter.” A well-known study asked why Bedouin communities in the Sinai desert traditionally wear black robes rather than white, given the heat. The answer: their robes are loose. The extra heat absorbed at the black fabric’s surface gets carried away by air moving up through the loose folds before it ever reaches the skin — a natural chimney effect. Worn loose, black and white performed almost the same.

The people we saw on the riverbank, though, were mostly in close-fitting T-shirts and tops — exactly the situation where colour matters most, because there’s no airflow to carry the absorbed heat away.

So what actually helps

Two things, and they work together:

• Loose fit — lets warmed air escape rather than sit against the skin
• Pale colour — absorbs less solar energy in the first place

Put them together and you get the best outcome. Tight and black is the worst combination; loose and pale is the best.

Why it matters more as summers heat up

None of this is urgent at 21°C. It becomes genuinely relevant on the hot, humid, high-sun days that are becoming more frequent — the kind Devon has seen more of in recent summers, and which places like Washington DC have been experiencing this year with real health consequences. On those days, the extra heat load from dark, tight clothing adds to a body that’s already struggling to lose heat, because high humidity limits how well sweat can evaporate. It’s a small, free adaptation — no cost, no infrastructure, just a wardrobe choice — that can make a real difference to comfort and, in extreme heat, to safety.