On Running launched the Ultra Vest Pro as the next generation of its first trail vest, at 200 €. One tester wore it through an entire UTMB 2025 build, around 170 km and up to 30 hours of cumulative effort, with zero chafing or discomfort. But French sources disagree on two concrete points: the vest's real weight, stated and measured at 300 g by some, yet listed at 225 g by a specialist comparison site, and its positioning, pitched sometimes as an ultra-distance vest, sometimes as a model for short to mid-length races.
© On Running, official photo used for editorial purposes
On Running Ultra Vest Pro: the vest that puts the Swiss brand on the trail map
On carved out a prime spot in the running market with its instantly recognizable shoes, but was almost nowhere to be seen in trail and ultra-distance. The Ultra Vest Pro changes that: it's the next generation of the brand's very first hydration vest, which debuted as the Ultra Vest 10L, tested by the French press back in 2023. This Pro version keeps the overall architecture (10 litres, removable waterproof pocket, customizable closure system) while making the two Hydrapak 500 ml flasks standard, where they used to be sold separately depending on the configuration.
The vest comes in three colours (white, black, fog) and pairs with a dedicated accessory, the Ultra Quiver, sold separately for carrying poles.
RunMorph's advice: for the same budget and a bit more capacity, the Salomon S/Lab Ultra 12 is still the benchmark of the ultra category, and it's significantly lighter. For shorter races on a tight budget, the waterproof On Running Ultra Jacket pairs nicely with this vest in a stripped-down setup.
On Running Ultra Vest Pro: the claims vs what you measure on the trail
Two discrepancies stand out when you compare the available French sources. The first is weight: the tester who wore the vest through a UTMB 2025 build measured about 300 g without flasks (65 g more for the Ultra Quiver), a figure consistent with the official international spec sheets. An independent specialist comparison site, however, lists 225 g for the same model, a 75 g gap that goes well beyond the usual difference between men's and women's versions or between sizes. Since we can't weigh the comparison site's sample ourselves, RunMorph goes with the best-documented value, where field test and official specs agree, around 300 g, and flags the discrepancy for transparency.
| Data point | Field test / official source | Comparison site |
|---|
| Vest weight (without flasks) | ~300 g | 225 g |
| Intended use | Ultra-distance, UTMB (170 km tested) | Short to mid-length races |
The second discrepancy is about marketing positioning. The most in-depth test available in French presents the Ultra Vest Pro as a vest built for ultra-distance, proven over an entire UTMB build. A more general partner roundup, on the other hand, describes it as designed for short to mid-length races, aimed at "fast runners". The two readings aren't incompatible: a vest can be minimalist AND go the distance, but you should know that the messaging around this product varies a lot depending on the source.
© On Running, official photo used for editorial purposes
Comfort and fit: a vest that rides high and disappears
The vest sits fairly high on the torso, like Salomon's benchmark models, which frees up the stomach area and boosts stability. The soft, wraparound mesh straps caused zero rubbing according to the tester, even on runs of more than 10 hours. Fit is dialled in with elastic cords offering two tightening levels at the front, plus side straps, for precise adjustment without pressure points.
The reported result after 170 km and up to 30 hours of cumulative effort during a UTMB build: zero chafing, zero discomfort, including on the chest where the two flasks sit. That's a notable result for a fabric rated as highly breathable and minimalist, two qualities that often mean more rubbing on other vests on the market.
Field test: storage and stability built for long self-sufficient efforts
On storage, the tester highlights a zipped back pocket you can reach while running, a rare detail on this kind of vest and especially handy for grabbing a jacket or gloves without stopping. The 10-litre back pocket, waterproof and detachable, lets you lighten the vest for shorter runs by simply taking it off. Up front, two pockets hold your fuel and a dedicated zipped pocket keeps your phone within reach with no risk of it falling out, a real reassurance on technical descents.
On stability, zero bounce, even fully loaded (mandatory kit, nutrition, water, clothing), whether on the flat, climbing or on steep, punishing descents. The Ultra Quiver, tested alongside, clips on and off easily, with quick access to your poles even mid-climb.
Where it works, where it falls short
Long runs and ultra-trail: its home turf, confirmed by the most thorough test, with comfort that holds up over 30 hours of cumulative effort without chafing.
Demanding races with mandatory kit: the 10-litre removable back pocket easily swallows the required gear list for UTMB-type races.
Short, fast races: around 300 g is decent, but not the most competitive in the category against sub-200 g vests built specifically for speed.
Frequent fuelling during a race: the back pocket you can reach on the move and the deep front pockets make managing nutrition easy without dropping your pace.
First few runs: expect a short adjustment period to memorize the pocket layout and fine-tune your own setup.
Watch out #1: a weight that varies significantly depending on the source
The field tester and the official international spec sheets agree on around 300 g without flasks, while a French comparison site lists 225 g for the same model. A gap like that matters in a category where every gram counts: trust the best-documented figure (field measurement + official specs) and check the actual weight before buying if grams matter to you.
Watch out #2: marketing positioning that shifts from one source to the next
The most rigorous test available in French validates the Ultra Vest Pro over a full UTMB build, while a partner roundup presents it as built for short to mid-length races. That's not necessarily contradictory, but if you compare several sources before buying, know that the messaging around this product isn't consistent.
On Running Ultra Vest Pro vs the Ultra Vest 10L, the generation it replaces
The first generation, tested in 2023, already had the Pro's overall architecture: removable waterproof back pocket, patent-pending customizable closure system, Hydrapak 500 ml flasks. The main change with the Pro version and its spring 2026 update is that the flasks now always come included in the price, where they used to be sold separately depending on the configuration. If you already own the previous generation, upgrading isn't essential; for a first purchase, the Pro is the obvious pick in the brand's current lineup.
On Running Ultra Vest Pro vs its direct rivals
Against the Salomon S/Lab Ultra 12, developed with elite athletes, the gap comes down mostly to weight: 205 g versus around 300 g for the Ultra Vest Pro, with slightly more volume (12 L vs 10 L) at the same 200 € price. The Salomon remains the technical benchmark of the ultra category; the On wins you over with its back pocket reachable mid-run, a feature the S/Lab Ultra 12 only added in its latest generation.
Against the NNormal Race Vest 5L, from the brand co-founded by Kilian Jornet and built on a radically minimalist philosophy (174 g, 5 L), the Ultra Vest Pro owns its roomier build and extra storage, designed for long self-sufficient efforts rather than pure performance over short distances.
Strengths
- Comfort and stability praised in a long-term test (170 km, up to 30 h of effort, zero chafing)
- Zipped back pocket you can reach while running, rare on this kind of vest
- Removable, waterproof 10 L back pocket to adjust your load
- Two Hydrapak 500 ml flasks included in the price
- Mostly recycled materials (85% polyamide on the back and pockets)
Weaknesses
- Weight (~300 g) above direct rivals like the Salomon S/Lab Ultra 12 (205 g)
- Weight figures differ between sources, check before buying
- Marketing positioning not always consistent from one source to another
- Short adjustment period needed to learn the pocket layout
Find the right training plan for your next ultra on RunMorph →
The RunMorph verdict: 8.3 / 10
The On Running Ultra Vest Pro proves the Swiss brand can go toe to toe with the trail vest benchmarks from its very first serious shot at the segment. Comfort and stability, validated over a full UTMB build without chafing, are right where they should be at this price. The vest stumbles on one objective point, a weight that stays above its best direct rivals, and on one point of clarity, sources that don't fully agree on its exact weight or its intended use. If you're training for long runs or an ultra, the equation works in its favour; if you want the lightest vest possible for short races, other options are a better fit.
Key takeaways
The On Running Ultra Vest Pro is a 10 L hydration vest at 200 €, with two Hydrapak 500 ml flasks included and a removable waterproof back pocket. It weighs around 300 g without flasks according to the best-documented field and official sources, although one comparison site lists 225 g for the same model. A full test over a UTMB 2025 build (170 km, up to 30 h of effort) found zero chafing, with 9/10 scores for comfort, stability and storage.
On Running Ultra Vest Pro FAQ
How much does the On Running Ultra Vest Pro actually weigh?
Around 300 g without flasks, according to the most detailed field test and the official international spec sheets. A French comparison site lists 225 g for the same model, a gap worth checking before buying if grams matter to you.
Are the flasks included with the On Running Ultra Vest Pro?
Yes, two BPA-free Hydrapak 500 ml soft flasks are included in the 200 € price, an improvement over some earlier configurations where they were sold separately.
Is the Ultra Vest Pro suitable for an ultra-trail like UTMB?
Yes, according to the most thorough test available in French, which documents its use over an entire UTMB 2025 build, about 170 km and up to 30 hours of cumulative effort, with no chafing or discomfort.
What's the difference between the On Running Ultra Vest Pro and the Ultra Vest 10L?
The Pro keeps the first generation's overall architecture (removable waterproof pocket, customizable closure system) and makes the two Hydrapak flasks standard in the price.
Is the Ultra Quiver included with the vest?
No, it's sold separately (around 65 g) and clips on and off the Ultra Vest Pro easily for carrying poles.