Which socks for trail and ultra running?
Written by Victor Michel — history enthusiast and passionate alpinist based in Chamonix. Published August 1, 2026 · Updated September 8, 2026
On a multi-hour ultra, blisters are often the first cause of dropping out, ahead of muscular exhaustion. Choose a sock for its lack of chafing seams and moisture management — never for cotton.
Compression: useful or marketing?
Light compression at the calf can reduce the feeling of muscular fatigue on long descents, but the effect stays modest compared with fabric choice and seam-free construction, which remain the two decisive factors for avoiding blisters over a multi-hour format.
Toe socks: who are they for?
Toe socks separate each toe to eliminate any inter-toe friction, a frequent cause of blisters on long formats. They require a break-in period before racing and don't suit every type of shoe.
Double-layer construction: another way to fight friction
Some models stack two layers of fabric that slide against each other: friction happens between the layers instead of directly on the skin. This is the approach used by Cimalp on its X2 Long sock, whose NANOGLIDE® fibres provide breathability and whose upper hem is designed to reduce calf compression — a different route to the same goal as toe socks (eliminating the friction point), without requiring a break-in period.
| Criterion | Recommendation | Why |
|---|---|---|
| Fabric | Merino wool or technical synthetic, never cotton | Moisture wicking, blister prevention |
| Seams | Flat or seamless sock | Avoid any friction point over several hours |
| Height | Mid-calf for protection against gaiter chafing | Compatibility with anti-scree gaiters |
| Compression | Light at the calf, optional | Muscular support on long descents |
| Thickness | Thin to mid-weight depending on the season | Trade-off between comfort and heat dissipation |
Editorial selection
Top 5 recommended socks for trail and ultra running
Five references, from the classic technical sock to the blister-prevention toe sock.
Compressport — Pro Racing Socks V4
Compression sock specialist for trail running, a reference for many ultra runners.
X-Socks / X-Bionic — Trail Run
Targeted ventilation zones, good moisture management over long formats.
Injinji — Trail Midweight
Toe sock, a reference against inter-toe blisters on ultra.
Falke — TK5 Trail
German brand specialising in technical socks, good cushioning underfoot.
Mons Royale — Trail Sock
Merino wool, good odour management on multi-day formats.
Independent editorial selection, with no commercial link or partnership.
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FAQ
Why never wear cotton in trail running?
Cotton retains moisture instead of wicking it away, which softens the skin and multiplies the blister risk over a multi-hour format.
What sock height for trail running?
Mid-calf is the standard: it protects against anti-scree gaiter chafing while remaining compatible with most trail shoes.
Are toe socks useful?
They eliminate friction between the toes, a frequent cause of blisters on long formats, but need a break-in period before racing and don't suit every shoe.
Should you change socks during an ultra?
On a 90 km and beyond, many runners plan a spare pair at a key aid station, especially after a water crossing or in high heat.
Merino wool or synthetic for socks?
Merino wool handles odour better on multi-day formats; synthetic dries faster in rain or after crossing a watercourse.