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Castelli Thermoflex Arm Warmer

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Item # CST0104

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Item # CST0104

Get rid of mountain-sized goose bumps with Castelli's Thermoflex Arm Warmers.

Turn your short-sleeve bike shirts into chilly-weather jerseys with the Castelli Thermoflex Arm Warmers. The soft fleece fabric covers your arms and wicks moisture, while elastic at the ends keeps the Thermoflex Warmers from sliding down. Castelli's scorpion logo adds pinchy detail.

  • Soft Thermoflex fleece
  • Moisture wicking
  • Elastic cuffs

Tech Specs

Recommended Use:
Manufacturer Warranty:
1 year

Size chart


Arm and Knee Warmers
Rider Weight 99.2 - 132.3lbs
(45 - 60kg)
132.3 - 154.3lbs
(60 - 70kg)
154.3 - 176.4lbs
(70 - 80kg)
Short Size XS - M S - M L - XL 2XL - 3XL
Short Size:
Take your typically cycling short or bib sizing for comparison.

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Happier arms

  • Familiarity: I've used it once or twice and have initial impressions
  • Fit: Runs large

These arm warmers are awesome! They do run long on the arm but don't seem to crunched up when you slide them up a bit. The gripper is awesome, and doesn't seem like it falls down at all.

Mind the gap

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

Only used these a couple of times but they are a major upgrade from the cheap ones I had previously. First and foremost, they do their job in keeping your arms warm AND they are comfortable. They stay in place and best of all they go up far enough so you don't have to deal with that unsightly gap between your jersey sleeves and your arm warmers, thus signaling to other cyclists that you either a) don't have euro cycling fashion sense b) you are a noob and/or c) you just don't care. Either way, they stay in place, keep you covered, and most importantly keep you warm. I will echo other reviewers in that they seem to run slightly long but I would much prefer too long to too short. I wish there was a better size chart, so for what it is worth my arm length is 48 cm (shoulder to wrist) and bicep is about 28cm in circumference. I went with the medium which fits well.

Great Buy

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

I got the small (5'4" and 115lbs female) and they fit perfectly. They do run a touch on the long side, which I personally like. They are great at blocking out a lot of the wind as well as keeping the arms warm. They don't slide down, either. Love them!

Great addition to the kit...

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

Not much you can say about an arm warmer that does it's job, which these definitely do. They may seem a touch thin, but they are very effective; though they tend to run a bit long. I bought a pair of XL's based on some reviews, but they were way too long; I'm 6', w/ average length arms, I guess - not a knuckle dragger. So I exchanged them for the L, and while they are still just a pinch too long, it's not enough to warrant a return, and risking the mediums being too short. They fit snug and seem not to want to creep down at all. Plus, red is rad.

Reliable and warm

  • Familiarity: I've put it through the wringer

These are great warmers. Not too expensive and easy to get on and off. Just make sure to get the right size they do run on the smaller side. My cycling club uses these castelli's and i love them. I would recommend buying these.

Avg. ride time: 13h 21m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Fit picture

I have thin arms and am 69" tall with arms of regular length--this is how the smalls fit on me. The warmers are stretchy, so you should actually be able to wear your regular size with these unless you've either been lifting weights or enlarging your arms with peanut butter cups.

I bought these in red--normally people go for black, but you can see that red should work pretty well with a lot of different kit. (In fact, completely mismatched kit in my case :D).

Fit picture
Avg. ride time: 13h 21m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Good warmers for chilly days

    Wore these on a cool (low 50s), damp, and very windy ride and my arms felt comfortable--they neither got too hot through a hard effort nor did they get chilled. Simply perfect. I have long sleeved jerseys but the arm warmers extend the use of my short sleeved jerseys deeper into the year.

    I normally wear mediums in Castelli but I have the usual cyclist's noodle arms and so bought these in a small and am glad I did. The warmer stayed put on my arm--no tugging or adjusting on the ride was required at all. The gripper was not too tight. They are oh-so-slightly longer than I needed, so the small can fit someone who is average height.

    I'm wondering how these fit. I'm a skinny...

    I'm wondering how these fit. I'm a skinny dude. 5' 11" 150#. Most medium size warmers (like Pearl Izumi)I've tried on are too large in the bicep. I'm thinking Castelli warmers might fit since their jerseys always fit small. Any input?

    Castelli usually fits about a size smaller than Pearl Izumi. I have to ask, though: what's stopping you from getting a small in the Pearl?

    If I remember right, the small Pearl Izumi was too tight in the lower arm and good in the bicep. I need something that is more evenly proportioned. I have a friend who has some medium Assos warmers that fit me perfectly but they are really expensive and hard to find. I figured since Castelli seems to be sized for thinner riders, they might fit me better than other brands.
    Any thoughts?

    Best Answer

    I Usually buy one size smaller in the arm warmers then my bib/jersey size. I wear a L in Castelli bibs and jerseys but for arm warmers, leg warmers, and vest I wear a size down which is a medium.

    Do you have to get a size larger tahn...

    Do you have to get a size larger tahn the jerseys and shorts?

    Best Answer

    The warmers are sized more on Arm size that jersey size so if you have muscular American arms you will need to size up if you have skinny climbers arms the sizes will be accurate. Good luck

    Great look and durable, but . . .

      Castelli stuff is always pretty fashionable and durable - I love the look of these with the Castelli logo on the wrists and they've worn very well, however a large is extremely snug on my muscular but not huge arms. I'm 6"3" and a lean 175 pounds. They are snug enough that the seams have left marks in my skin for hours after I've removed them and they've even caused some nerve interference in my left bicep. Who knows, maybe I'm just getting old.

      Great look and durable, but . . .