Castelli Nano Flex 3G arm warmers review

A 'goldilocks' performer in my testing, the Nano Flex 3G arm warmers are high performers in every regard

Castelli Nano Flex 3G arm warmers
(Image: © Josh Croxton)

Cyclingnews Verdict

Others have a more premium feel, but the functional performance of Castelli Nano Flex 3G arm warmers make them some of the best


  • +

    Wind and water protection is among the best

  • +

    Great balance between warmth and breathability

  • +

    Inner and outer silicone gripper equals double-secure hold


  • -

    They are more expensive than the main competitor, which also happens to be better

  • -

    Slight overcompression of upper arm

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The Castelli Nano Flex 3G Arm Warmers are one of a host of accessories made by the Italian brand and put simply, they take Castelli's fleece-lined, water-resistant Nano Flex 3G material and shape them into cylindrical tubes of arm-warming goodness. 

When it comes to cold-weather cycling clothing, few brands are more established than Castelli. Join any local club ride anywhere in the world and you can bet the brand's iconic scorpion logo will be along for the ride. The brand is popular, and for good reason; it makes great quality cycling clothing that is a regular feature in our buyer's guides. 

Today's focus, the Nano Flex 3G arm warmers, already feature in our guide to the best arm warmers for cycling, but while we can back up that inclusion with years of testing behind the scenes, I've spent the past few months wearing them alongside a few of their closest competitors such as the Assos Evo 7 arm warmers, the Sportful NoRain arm warmers and others to see which are the best, or why you might buy one instead of the other. 

They are priced at £40.00 (USD59.99 / EUR39.95), which is in a similar ballpark to the competition, but a little more expensive than the Assos option. 

Design and specification

The Castelli Nano Flex 3G arm warmers come in four sizes - S, M, L and XL - and two colours. The first colour is an obvious choice of black, which from a style perspective goes with everything. The second is in my opinion a slightly nicer choice of navy blue. This is the colour I opted for, and I've been using them on and off for about a year. Unlike the Assos pair, these arm warmers aren't left-right specific in their fit. They do have printed 'Castelli' and 'Nano Flex' logos that would be upside down if worn on the wrong arms, but this won't affect how they fit and perform. 

As highlighted above, they are made almost entirely from Castelli's Nano Flex 3G material. This is a material that features in some of Castelli's most premium winter wears, including Sorpasso ROS Wind bib tights. It is fleece-lined on the interior face, making it soft against the skin, and each fibre is treated with a water repellent coating, helping it to keep water out. 

The only area of each arm warmer that's not made using this material is the elasticated band at the upper arm, this is a 15mm thick strip of black material, with 5mm of silicone on the inner face and a trio of Castelli logos on the outer face, also printed in silicone, to help the arm warmers grip onto the sleeves of jerseys, further helping them to stay up. 

At the wrist cuff, the Nano Flex 3G material is folded over, and all seams are double stitched to promote durability. 

Castelli Nano Flex 3G arm warmers

Silicone grippers exist on both the inside of the upper arm, in the form of a band, and the outside in the form of Castelli logos (Image credit: Josh Croxton)


In terms of the feel, the Castelli Nano Flex 3G arm warmers don't match Assos' premium softness, but that doesn't mean a reduction in performance. They feel ever so slightly thicker, but the warmth, water resistance, wind resistance and breathability are entirely indistinguishable. They aren't quite as warm as Sportful's NoRain, but they do breathe better and they lasted longer before wetting out in a test under a running tap. 

Like Sportful (and unlike Assos), the Nano Flex 3G arm warmers get a silicone grip consideration at the top. This is both inside and out, meaning there have been no questions about whether they will stay up on my arms. They are ever so slightly tighter on me than the Assos option, and they leave a slight compression mark when you take them off, but they're not quite as tight as Sportful. Another similarity with Sportful is their ability to be worn on either arm comfortably. This means they are quick to get on whilst riding as there's no faffing around to find which is which. 


In my experience of testing them against the Sportful NoRain and Assos Evo 7, the Castelli Nano Flex 3G arm warmers aren't the best, but they are a close 2nd and they have their unique selling points.

They are equal best for water resistance, wind protection and breathability in my testing, but they are slightly less premium in their finish and their feel, while also being a touch more expensive. However, they come in a design that's slightly tighter, which when paired with silicone grippers inside and out, might swing the decision for those who are worried about upper arm security. 

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Josh Croxton
Tech Editor

As the Tech Editor here at Cyclingnews, Josh leads on content relating to all-things tech, including bikes, kit and components in order to cover product launches and curate our world-class buying guides, reviews and deals. Alongside this, his love for WorldTour racing and eagle eyes mean he's often breaking tech stories from the pro peloton too. 

On the bike, 30-year-old Josh has been riding and racing since his early teens. He started out racing cross country when 26-inch wheels and triple chainsets were still mainstream, but he found favour in road racing in his early 20s and has never looked back. He's always training for the next big event and is keen to get his hands on the newest tech to help. He enjoys a good long ride on road or gravel, but he's most alive when he's elbow-to-elbow in a local criterium.