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Castelli Thermolite 9 Socks

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Item # CST003H

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Item # CST003H


We're big fans of Castelli's Thermolite 9 socks for a few reasons. First, they're fantastic, durable, comfortable cycling socks. Second, their name tells their whole story. They're thermally insulated socks, but only mildly so, excellent for cool-weather riding conditions, and not so insulating as to be uncomfortably warm when the sun comes out or when the pace cranks up. Thermolite is a medium-density, hollow-core polyester material that promotes breathability and moisture transfer to preserve the comfort of your feet, while still insulating them enough to fend off the chill of fall days. The midfoot is supported by an anatomic band of fabric that prevents cramping and hotspots. The socks have a nine-centimeter cuff, come in the sizes S/M, L/XL, and XXL, and in the colors Black or White.

Tech Specs

Thermolite polyester
9 cm
Recommended Use:
cool weather cycling
Manufacturer Warranty:
30 days

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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Here's what others have to say...

5 5

Tan lines for days

  • Familiarity: I've used it several times
  • Fit: True to size
  • Height: 5' 3"
    Weight: 120 lbs

These are my go to socks for everyday warm weather riding. The 6" cuff is the perfect height to show off another cycling tan line.

5 5

Great Socks!!

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

These are high quality - long lasting socks.
You won't even know you have them on.
They are so comfortable and wick your feet dry.
My question is with quality gear like this why does some nincomepoop insist on putting the two socks together with a push through plastic T-bar thing that always snags the socks or other garment. I hate it when my clothing has label tags in the neck area, or some other uncomfortable area and if you tear the tag out you tear the garment. In my case here I pulled the two socks apart that were attached with the T-Bar plastic thing that went through both socks when I pulled it out it made a run like in a nylon stocking. Now that sucks!!!!

5 5

Best winter sock

  • Familiarity: I've put it through the wringer

Absolutely love these socks. Not overly bulky like wool socks, but keep the feet nice and warm. Also very durable. Had several merino wool socks that have quickly developed holes, these have lasted all winter for me and there's no sign of any holes developing. Nothing bad to say about these socks.

5 5

Castelli never disappoints

What can I say, Castelli clothing never lets me down. These socks fit perfect and feel great.