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Item # CST2610

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Item # CST2610

Sock it to 'em.

The Castelli Free 9 Sock is to regular socks as space shuttles are to balsa-wood gliders—the basic design is similar, but everything that matters is totally different. The Free 9 is woven from Meryl Skinlife fibers, which are engineered to be antimicrobial, highly breathable, and moisture wicking, so your feet stay fresh, dry, and comfortable. A high-density woven band under the arch supports your foot and prevents slippage without adding any extra thickness, a flat toe seam prevents irritation, and an open mesh panel at the cuff increases airflow to provide unbeatable ventilation.

  • Meryl Skinlife fibers
  • High-density woven arch band
  • Flat toe seam
  • Open mesh cuff panel
  • Antimicrobial
  • Breathable and moisture wicking

Tech Specs

Meryl Skinlife
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.

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Avg. ride time: 2h 52m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

So nice we made them the kit standard

  • Familiarity: I've used it several times
  • Fit: Runs small
  • Size Bought: l-xl

In previous years we dealt with custom socks. It took a lot of time, high minimums and frankly the quality was just okay. We chose the Castelli Free 9 and it works great with the kit design. Now we look and feel great and don't have to mess with excess stock. This will be our strategy going forward.

Benchmark summer socks

  • Familiarity: I've put it through the wringer
  • Fit: Runs small

Italians know auto racing, cycling, fashion, and.... socks. Castelli takes a lot of pride in their sock manufacturing ability.

These are benchmark hot-weather training/racing socks.

(#1) Free 9's are amazingly well ventilated along the top of the foot and all the way around the shin to the top of the cuff. Very clever/sophisticated seamless sock manufacture here.

(2) Made in Italy from top-of-the-line european textile (meryl skinlife); silver infused and thus bacteria/odor resistant. Super moisture wicking. And noticeably soft and comfy.

(3) They look great. Looks are important.

(4) 9 cm is the min height for road socks. (6 cm looks too low).

These are a must in hot weather if you ride in Castelli kit. And even if you don't.

Sizing: The official sizing chart at the Castelli website is best:
Cycling shoe size: 36-39 = S/M
Cycling shoe size: 40-43 = L/XL
Cycling shoe size: 44-47 = 2XL

I wear a size 45.0 in Shimano (321's). The 2XL fit me perfectly.

Tight Fit

  • Fit: True to size

After trying a couple of brands I have found the the Free 9 socks have an appeal that I enjoy while riding. They are not to hot for the humid weather that I ride in most of the summer and fall. They have lasted a couple dozen rides without losing shape. The feel in the shoe is like a second skin with the protection for the 100km rides.

Great socks

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

My new favorite socks. The L/XL fit my 10.5 feet perfectly. Fabric feels soft to the skin. They are light and airy - perfect for summer or any non-cold day. They look very sharp too!

The best summer socks!

  • Familiarity: I've put it through the wringer

I have four pair of these socks. They are the best summer socks I have owned. I have tried socks from companies like Rapha, Swiftwick, and Defeet, and these are the best. They fit like a good cycling sock should. They don't bunch up and they are not too loose. If you have a nice pair of cycling shoes, I highly recommend getting a good pair of socks so your shoes will fit like they should. I wear a size 45 in Sidi and the L/XL fits perfectly.

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.

Great lightweight sock

  • Familiarity: I've put it through the wringer

I am a women's 9 and I bought a L/XL, though I was weary of the size since a women's 9 is usually a men's 7. Originally this footbed on the sock was way too long, but now fits perfectly after one machine-wash on delicate (had only handwashed before). The band can be rather snug and the logo stretched if you have bigger legs but the sock won't fall down! Great fluoro color, no bunching, and very breathable.

Avg. ride time: 11h 4m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Nice socks

  • Familiarity: I've put it through the wringer

These have been great so far this summer. I wear a 9-9.5 size shoe and ordered the L/XL size for these socks. I would go with the smaller size if I order more - the foot area of the sock is just a little too long for my preference (not the height of the sock, the foot area).