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Item # CST003F

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Item # CST003F

Proven in labs and stuff.

Extensive clinical study and mounting evidence in various fields of research has led scientists around the industry to conclude that Merino wool is rad. It's naturally odor-resistant, extremely breathable, and the insulating archetype that all these hollow-core synthetic yarns are mimicking. When fashioned into a tube, ribbed around the ankle, and reinforced to support the midfoot arch, merino provides a platform for a fantastic cool-to-cold weather cycling sock, and that's exactly what the Castelli Merino Socks are.

Tech Specs

70% merino wool, 15% nylon, 15% elastane
9 cm
Recommended Use:
Manufacturer Warranty:
1 year

Size chart



Castelli Socks
US Men's shoe
4-7 8-10 11-14
US Women's shoe
5-7 8-10 11-12
How to Measure:
For best results, take measurements over your underwear.

Reviews & Community


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Favorite winter sock

  • Familiarity: I've used it several times
  • Fit: True to size

The fabric and fit are great, but what I like most is that the thickness on the bottom wraps up over the toes. Other winter socks I've tried don't have this, and my toes get cold. These are the only winter socks I reach for now.
I wear size 46 Pearl Izumi shoes - 11 or so in Nike running shoes. The L/XL in these socks fits just right, but I don't put them in the dryer.


  • Familiarity: I've put it through the wringer

Made in Italy, these Castelli socks are a work of art. The quality is 10/10. Really, just wait till you receive them.

By the way... wool offers the best wicking material, insulates yet breathes, all with zero odor (naturally). Wool is a superfabric!

Sizing: I wear a 45.5 shoe in Sidi and Shimano. The L/XL just fit but the XXL fit better. Wool socks do shrink slightly. If you wear a 45+ shoe, definitely buy the XXL.

Long lasting too!

  • Familiarity: I've put it through the wringer
  • Fit: True to size
  • Size Bought: L/XL

Most durable and warmest wool cycling socks I've ever owned, Other brands shrink too much or lose their nap/thickness. Lots of miles on these, spring, fall and winter! I use L/XL with shoe size 43.

These reviews raving on SOCKS cracked me

  • Familiarity: I've put it through the wringer
  • Fit: True to size
  • Size Bought: L/Xl (45 shoe)

up until I got a pair last year. They are pretty much the best socks ever. I got 4 more pair because I wind up using them off the bike as much as on. I live in Florida so they are a bit much 6-8 months out of the year but you won't be disappointed if you are looking for a thicker, well made sock for chillier days.

favorite socks

  • Familiarity: I've put it through the wringer
  • Fit: True to size

awesome fit, perfect length, nice cushion on the sole but not too much...i'm always hunting for better socks and these are hard to beat.

Avg. ride time: 0m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Best Socks I've Used

  • Familiarity: I've put it through the wringer
  • Fit: True to size
  • Size Bought: Large

So far these are the best socks I've used. They're extremely comfy to wear, but they are quite thick so if your shoes are to tight as they are, you might want to opt for a thinner pair, so far I've had no problems. Surprisingly I've worn them up to 75F before they've gotten uncomfortably hot.

I got Large, and I currently wear a 10-10.5

Best Socks I've Used
Unanswered Question

I've read several reviews on BC's sister web site - Competitive Cyclist - that indicate the white socks aren't pure white as shown. Rather, they're described as "off-white" or "cream." Can someone from BC or who owns these weigh in? Thanks.

very nice socks

  • Familiarity: I've used it once or twice and have initial impressions
  • Fit: True to size
  • Size Bought: xxl - size 11 foot

I ordered one pair of all of the Castelli socks. I returned all of the others as they more closely resembled tube socks. These socks have a nice angle that anotomically fits the angle from foot to leg and doesn't crease in that area when the foot dorsi flexes. The wool is soft and stretchy. Too bad the others aren't made like this pair.