TIMING
Go early or late
UK heat advice says to plan physical activity for the early morning or evening, when it is cooler, and to avoid direct sun between 11am and 3pm.
Plan a warm runWHAT THE RESEARCH SAYS
Dress for
the sweat.
On a warm run, sweat does the cooling.
Check a top
UPF 40+to be labelled sun-protective in the UK
It works when it can evaporate. Running kit promises to help, but the research is more mixed than the labels. What matters most is often when you run, how much skin is covered and how the fabric handles the sun.
At a glance
- Run in the cooler hours
- Light, loose and breathable
- Fabric weave beats hype
- Kit helps, timing helps more
5 of 20
Light-to-moderate studies finding a core-temperature difference
Of 20 studies at light-to-moderate intensity, only five found significant differences in core temperature between synthetic and natural fabrics.
FABRIC TRIALS · SPORTS MED OPEN, 2022
≈ 5× more
Dark clothes vs white, for sun protection
DermNet says dark coloured clothes give around five times more protection from the sun than white clothing, because dye helps absorb ultraviolet rays.
COLOUR · DERMNET
TWO NUMBERS WORTH KNOWING
The fabric matters
less than you'd think.
One figure from a review of sports-clothing trials,
one from dermatology guidance on colour.
The same review notes that 72% of the studies it covered included male participants only, so the evidence for women is thinner (Sports Medicine Open, 2022).
A QUICK TOP CHECK
How much sun
gets through?
Pick a top to see what dermatology guidance says about how well it blocks ultraviolet light. The bar shows the level of sun protection.
Based on DermNet's sun protective clothing guidance and the UKHSA ultraviolet radiation FAQ. General information, not medical advice.
THE SHORT ANSWER
Timing first,
then the fabric.
Sweat evaporation is the body's main way to shed heat.
Clothing can help it, or get in the way.
FABRIC
Polyester or cotton?
A 2022 review found that in hot, dry lab trials synthetic and natural fabrics made no significant difference to core temperature or performance. Humid trials were more mixed.
See the numbers
SUN
Hold it to the light
The less light that gets through a fabric, the more UV it blocks. Tight weaves and darker colours protect more; stretched or wet fabric protects less.
Check a top
FOUR HABITS FOR WARM RUNS
Cooler runs,
fewer surprises.
None of these needs new kit. They draw on UK hot-weather advice and what the clothing research actually found.
Check the forecast
UK guidance suggests checking forecasts and planning activity for when it will be cooler, usually early morning or evening.
Wear less, loosely
Remove unnecessary layers and choose lightweight, breathable clothing so sweat can evaporate.
Cover up in strong sun
Between 11am and 3pm UV is highest. UK advice suggests a wide-brimmed hat, sunglasses and sunscreen on bare skin.
Drink as you go
UK advice is to drink fluids regularly, especially when active, so your pee is a pale straw colour.
LIGHT OR DARK?
A colour
trade-off.
UK heat advice suggests lightweight, loose-fitting, light-coloured clothes. Dermatology guidance says darker colours block more UV than the same fabric in white.
Both can be true: the right choice depends on whether heat or strong sun is the bigger issue on your route. Whatever the colour, a tight weave, a loose fit and a dry top protect best, and stretched or worn fabric protects less.
Questions
Questions people ask
Is polyester better than cotton for running?
Not clearly. A 2022 review found no significant differences in core temperature or performance between synthetic and natural fabrics in hot, dry lab trials, and only five of 20 lighter-intensity studies found a core-temperature difference.
What does UPF mean?
Ultraviolet Protection Factor shows how much UV is reduced passing through fabric. A UPF 20 garment lets through 1/20 of the UV that reaches bare skin. In the UK only clothing rated UPF 40 or more can be labelled sun-protective.
Does a sweaty top still block the sun?
Less well. DermNet says many fabrics lose protection when wet, some by as much as half, especially cotton.
When is the best time to run in hot weather?
UK heat guidance suggests the early morning or evening, when it is usually cooler, and avoiding direct sun between 11am and 3pm when UV is highest.
Should I wear light or dark colours?
For heat, UK advice suggests light colours. For UV, darker colours of the same fabric protect more. Choose by the bigger risk, and cover exposed skin with sunscreen.
Sources
Where the facts come from
- GOV.UK (UKHSA): Beat the heat, staying safe in hot weather
- NHS: Heatwave, how to cope in hot weather
- GOV.UK (UKHSA): Ultraviolet radiation frequently asked questions
- DermNet: Sun protective clothing
- Sports Medicine Open (2022): The role of sports clothing in thermoregulation, comfort and performance during exercise in the heat
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