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CastelliFree 9 Sock

Sale 30% Off$11.87 $16.95

Item # CST2610

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Item # CST2610

Free 9 Sock

The Castelli Free 9 Sock is woven with Meryl Skinlife antibacterial fibers. This moisture-wicking, breathable fabric pulls sweat away from your skin to keep you dry and comfortable. The top of the foot is a diaphanous web, ultra-thin and extremely breathable. In the middle of the foot, the arch area, there is a high-density band woven in. You won't notice any difference in thickness, but you will feel like the sock is becoming one with your foot rather than sliding around between your foot and your shoe. The toe has a flat seam for comfort and the cuff at the top is folded over to keep the sock from slipping. Castelli also added an open mesh panel to the cuff to allow air to move freely through the sock.

  • Castelli's ideal sock for warmer summer rides
  • Meryl Skinlife fibers are breathable, wick moisture, and dry quickly
  • High-density woven arch band improves foot support
  • Flat toe seam all but eliminates friction, chafing, or irritation
  • Lightweight mesh on the top of the foot and ankle promote ventilation
  • Antimicrobial yarns help reduce odors
Tech SpecsSize
Tech Specs
Meryl Skinlife
Recommended Use
Manufacturer Warranty
1 year


US MEN'S SHOE SIZE 4 - 6.5 7 - 10 10.5 - 13
EU MEN'S SHOE SIZE 36 - 39 40 - 43 44 - 47
US WOMEN'S SHOE SIZE 4 - 7 7.5 - 9.5  
EU WOMEN'S SHOE SIZE 35 - 38 39 - 41  


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Breathable, Look Good

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

Good socks, nice and breathable and they stay in place. These do fit tight with compression keeps them from moving, so keep that in mind if you're between sizes. These aren't super fancy but a good choice to match your kit.

Unanswered Question

My feet is size US 10 and Euro 44. What size of castelli sock should I pick up? XL or XXL?

Pretty Good

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

Love the material for hot days, but runs a little small. I'm a 14 shoe size and bought a XXL and it's still a little small -- but manageable.


  • Familiarity: I've used it several times

This is a really great cycling sock, they are lightweight, keep me cool, and look great! Would definitely recommend and will pick these up again in the future!

Best Cycling Socks

    The sizing is spot on, and the quality is as expected with any piece of Castelli apparel. Snug fit and smoother material prevents hot spots on long ride, and the high quality definitely makes them on of the longer lasting cycling socks I’ve owned.

    thin, comfy sock

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

    These socks are thin, breathable, and comfortable. I of course bought these for road cycling, but have also used them as a liner sock on a through-hike because of the qualities I mentioned. I agree with John that they'd look a little better if the cuff was a bit longer.

    I wear a 47 EU cycling shoe / US 12 casual shoe and the XXL feel just right.

    Completes the Kit

    • Fit: True to size

    Bought these socks to go with my Castelli kits for summer riding. Super thin and comfortable socks that offer superior wicking. My only complaint is that they are on the short side, but still a great sock.

    Great sock

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

    Comfortable with a combination of support and lightweight. Really like the length as well.

    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 are famous for auto racing (Ferrari), cycling, fashion, and.... socks. Italy is famous for their sophisticated 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 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.

    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.

    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).

    These socks though!!!

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

    Yeah, just buy a pair or two, or 5 like I did.

    Fit great, look great ride well.