OS2O Fast&Light Review: The Kit I Won an Ultra In
The first 45 km: climbs are my jam
Climbing is my strength, and I love it. This course is descent-heavy, so I leaned on my poles, stayed really focused and kept it joyful. That joy helped so much.I started in the light pink OS2O Axis Long T-Shirt and the OS2O Nimbus Shorts, with the OS2O StretchLight Trail Belt paired with my vest to stash my extras. The belt sat firm the whole way and never bounced.
45 km: the drop-bag change
At my drop bag at 45 km, I changed into the purple OS2O Blade T-Shirt and wore it to the finish. The toe socks stayed on for the entire race, and so did the belt.
The finish: disbelief and pure joy
I only realised near the end that I was leading the women’s race. Crossing the line in Argelès-sur-Mer as first woman, in a race I’d entered 2.5 weeks earlier, was pure joy and total disbelief. You can see it on my face in the finish photos.
Since then, the OS2O piece I reach for most is one I didn’t even race in: the purple OS2O Phantom Grid Jacket. More on that below.
The OS2O kit, piece by piece
OS2O Phantom Grid Jacket Woman: my favourite jacket, full stop
Shop: OS2O Phantom Grid Jacket Woman · OS2O lists Polar Stretch Grid fabric, YKK zip side pockets, thumbholes and a hood collar that covers mouth and nose.
I’m obsessed with this piece. It fits beautifully, it has two zip pockets (thank you, OS2O, for pockets), and it has a built-in buff and hood, so I’m not digging around for a neck warmer on a cold summit at sunrise.
It’s the perfect mid-season layer for early starts in the Pyrenees, and it’s about to become my go-to layer over my skimo race suit this winter.
OS2O Axis Long T-Shirt Women: my top for the first 45 km
Shop: OS2O Axis Long T-Shirt Women · OS2O lists it at 84 g in size XS, with mesh panels on the back, underarms and sides.
I started the race in this light pink long sleeve and wore it for the first 45 km. It’s light and breathable, and the fit is great.
OS2O Blade T-Shirt Women: 45 km to the finish, not a single chafe
Shop: OS2O Blade T-Shirt Women · OS2O lists it at 65 g in size XS, with a rear mesh panel and UPF 50+ fabric.
I pulled this tee on at my 45 km drop bag and wore it to the finish line, and it held up. It wicked sweat on the climbs, I had zero chafing, and the sleeves are so light it feels like they’re not there.
The cut suits women’s bodies, especially around the midsection. And purple is my favourite colour, which helps, but it’s also bright enough that you’re easy to spot on the trail.
OS2O Nimbus Shorts Women: feels like wearing nothing
Shop: OS2O Nimbus Shorts Women · OS2O lists them at 62 g in size XS, with a built-in inner brief and a wide side split.
I wore these light, skin-toned shorts for the first 45 km of the race. The built-in brief actually holds you in, and the fabric is so lightweight it doesn’t ride up. They feel like nothing, which is exactly what you want in a long race.
My one wish: a small pocket for a key or something small. On race day, the OS2O belt solved that.
OS2O StretchLight Trail Belt: the best I’ve ever used
Shop: OS2O StretchLight Trail Belt · OS2O lists four pockets, pole straps and a seamless stretch fabric.
I wore this belt for the whole race, paired with my vest, to stash extras. It’s the best belt I’ve ever used. It sits firm and doesn’t bounce, thanks to the style of the fabric, and it adds the pockets my shorts don’t have.
OS2O Merino Coolmax TRAIL Toesocks: I wore them for the whole ultra
Shop: OS2O Merino Coolmax TRAIL Toesocks · OS2O lists a merino wool and Coolmax blend.
I swear by toe socks, and these went the full distance with me.
My wishlist for OS2O: an even taller version. For mud, scree and winter, I’d love more coverage up the leg.
Check out my OS2O Haul below! Thank you again OS2O Fast&Light team!
OS2O O2 Waterproof Trail Speed Zip Jacket 30k Woman: passed the mandatory gear check
Shop: OS2O O2 Waterproof Trail Speed Zip Jacket 30k Woman · OS2O lists it at 138 g in size XS, rated 20,000 mm waterproof, with a rear zip gusset so it fits over a vest.
A waterproof jacket was mandatory kit for the race, and this one passed every check. When I needed it, it worked a charm. It’s light enough to live in my vest without me noticing it’s there.
My verdict on OS2O Fast&Light
OS2O’s Fast&Light kit carried me to a win in a race I entered 2.5 weeks out. The long sleeve, shorts, and tee disappeared on me, the belt and toe socks went the whole race, the rain jacket ticked the mandatory box, and the hooded midlayer has become the piece I reach for every day.
| Piece | Tested | What I loved | What I’d change |
|---|---|---|---|
| Hooded midlayer | Training + summit mornings | Fit, two pockets, built-in buff and hood | Nothing yet |
| Race tee | 45 km to the finish | Wicking, no chafing, weightless sleeves, women’s cut | Nothing |
| Shorts | First 45 km of the ultra | Built-in brief that holds, doesn’t ride up | Add a small pocket |
| Toe socks | The whole ultra | Toe socks done right | Make an even taller version |
| Rain jacket | Mandatory race kit | Passed the gear check, worked a charm | Nothing |
| Light pink long sleeve | First 45 km of the ultra | Light, breathable, great fit | Nothing |
| Running belt | The whole ultra, with my vest | Sits firm, no bounce, extra pockets | Nothing |
Who it’s for: trail runners and ski mountaineers who want light, technical kit that’s actually cut for women.
My wishlist for OS2O: a pocket in those shorts, and even taller toe socks for mud, rocks, and winter.
Next up, the midlayer goes over my race suit for the skimo season. I’ll be back with an update in the winter, as I race on the ISMF World Cup Skimo circuit and hopefully, Pierra Menta 2027
Want help training for your first ultra or skimo season? Read More Here· New to skimo? See this guide.
