Which T-shirt for trail and ultra running?
Written by Victor Michel — history enthusiast and passionate alpinist based in Chamonix. Published August 1, 2026
A trail T-shirt is chosen on three criteria: fast sweat-wicking, freedom from chafing over several hours of effort, and odour-control treatment for multi-day formats. Cotton, which retains moisture, is to be avoided.
Short sleeves or long sleeves?
UTMB rules require a mandatory 2nd warm layer (see the mandatory gear): a long-sleeve top of at least 180 g, or a 110 g 1st layer paired with a water-repellent windbreaker. Outside this regulatory constraint, short sleeves remain the default choice for the base layer, topped with a windbreaker or jacket depending on the weather.
Synthetic or merino wool?
Technical polyester dries faster and generally costs less; merino wool handles odour better on multi-day formats (90 km and beyond) but dries more slowly and wears out faster under intensive use. On a one-day format, synthetic remains the most common choice among elite runners.
| Criterion | Recommendation | Why |
|---|---|---|
| Fabric | Technical polyester or merino wool, never cotton | Fast sweat-wicking, drying on the move |
| Odour-control treatment | Silver salts or merino fibres | Comfort on long or multi-day formats |
| Seams | Flat, positioned away from chafing zones (shoulders, underarms) | Avoid irritation over several hours of effort |
| UV protection | UPF 30 to 50 | Prolonged exposure at altitude, stronger radiation |
| Cut | Fitted without excessive compression | Comfort under a trail vest worn for several hours |
Editorial selection
Top 5 recommended T-shirts for trail and ultra running
Five references, from pure technical polyester to merino wool, for short formats as well as ultra-distance.
Salomon — Sense Aero
Competition cut, very lightweight and breathable fabric, a reference among elite runners.
Compressport — Training T-Shirt
Light-compression specialist, flat seams, good value for money.
Cimalp — Argentieres H
French brand founded in 1964, SMARTWARM® and CIMAFRESH® fabrics (silver-salt odour-control treatment). Tested over 3 outings of 25 km by an independent Spanish tester, who noted the weight as somewhat excessive for ultralight use.
Odlo — Blackcomb / Essentials range
Swiss base-layer specialist, good synthetic/breathability trade-off.
Raidlight — Activ Dry / Wintertrail
French brand specialising in ultra-distance, ranges dedicated to both heat and cold.
Independent editorial selection; the Cimalp mention relies on a verified third-party test (see site sources), with no commercial link.
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FAQ
Can you run an ultra-trail in cotton?
No. Cotton retains moisture instead of wicking it away, which chills the body when you stop and favours irritation. A technical fabric (polyester) or merino wool is essential.
Are long sleeves mandatory for the UTMB?
The mandatory 2nd warm layer can be a long-sleeve top of at least 180 g, or a 110 g 1st layer paired with a water-repellent windbreaker — see the mandatory-gear breakdown.
Merino wool or synthetic for a 90 km?
Merino wool handles odour better over time, a real advantage on multi-day formats or at crowded aid stations. Synthetic dries faster in rain or heavy sweating.
What is a silver-salt odour-control treatment?
An antibacterial treatment built into the fibre that limits the growth of odour-causing bacteria, allowing the same T-shirt to be worn longer without discomfort — useful on multi-day formats.
Do you need a compression T-shirt for trail running?
It's not essential, but light compression across the torso can limit chafing under a trail vest worn for several hours.