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Castelli Nanoflex arm warmers



Versatile piece of kit made even more versatile by the water repellant coating

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

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Starting with a standard pair of their Thermoflex armwarmers and coating it with millions of silicone 'nanofilaments', Castelli have created a water repellent fabric called Nanoflex that causes raindrops to bead off of the fabric as you are riding keeping you drier for longer. That's the theory; and the practice?

Well, in practice the Nanoflex arm warmers, like the Nanoflex knee warmers we tested recently, are pretty impressive too. Light rain and road spray are just blown off the material by the wind as you travel along. This process works in heavier downpours until the fabric gets overwhelmed and once wet the thermal fleece fabric keeps you warm so it's no real problem. In the dry they work exactly the same as the standard Thermoflex warmers they are based on. While warm they are not overly so and can be worn on spring/autumn mornings without the fear of overheating.

The Thermoflex material offers thermal protection using a fleece inside which also provides comfort as well. The fit is close with the size tested covering from wrist to armpit on me, there are no size guides on Castelli's website but to give a little idea of how they measure up my arm length is 46cm and a 18cm diameter bicep. They stayed put all ride thanks to silicone grippers either end and the fact they are so long stops that annoying gap between armwarmer and jersey sleeve happening.

Price wise we're looking mid to high end here at just over the thirty quid mark and being just a couple of pounds extra than the standard Thermoflex the Nanoflex coating is a worthwhile extra. The de rigueur colour choice of white, black or red is available in sizes from small to extra large.

All in all the water resistant coating makes good sense especially at this time of year when a full waterproof jacket is too warm in the rain but paired with a gilet these warmers keep the worst of the dampness at bay. Thin enough to be used as a layer in the minus temperatures winter throws at us under a softshell or jacket coupled with being able to use them in spring/autumn without overheating makes them versatile and probably one of the most used bits of kit in your wardrobe.

There is a downside though as ever, a large seam runs the full length which can get irritating after a while plus the graphics don't look like they will stay attached very long and look a bit rubbish once the material is stretched over your arm.


A veratile product that should be of use for at least 75% of the year in the UK. The water repellent coating is impressive and works in all but the heaviest rainfall but by this stage you'll probably be thinking about a waterproof jacket anyway. A good fit though with a reasonable price tag which is only let down by that overly large seam.

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Make and model: Castelli Nanoflex arm warmers

Size tested: Large

Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?

A standard armwarmer combined with Castelli's water repellant Nanoflex technology to create a more versatile piece of apparell. It does give them an edge over the competition and a solution to a problem you'd never realised needed solving.

Tell us some more about the technical aspects of the product?

A silicone coating provides the water repellent finish which keeps light rain and road spray out.

Rate the product for quality of construction:

Look well made and the stitching held up to the armwarmers being pulled on and off plenty of times

Rate the product for performance:

The water resistant coating works as well as expected

Rate the product for durability:

Everything looks fine except for the naff logos

Rate the product for comfort, if applicable:

That irritating seam

Rate the product for value:

The price is about on par with what you'd expect, there are more expensive options out there without the water resistance - it is worth looking around though because we've seen them substantially discounted on-line

Tell us how the product performed overall when used for its designed purpose

In the dry these armwarmers are pretty standard fair, doing a good job of keeping you warm and pack down small in your pocket. When the weather is wet though having the water repellant coating works well and up to the level expected for a water resistant product

Tell us what you particularly liked about the product

The fit and the Nanoflex technology

Tell us what you particularly disliked about the product

The large seam was uncomfortable after a while. Many other armwarmers I have worn have a seam half the size.

Did you enjoy using the product? Yes

Would you consider buying the product? Not really

Would you recommend the product to a friend? Possibly

Overall rating: 7/10

About the tester

Age: 32  Height: 180cm  Weight: 78kg

I usually ride: Genesis Flyer  My best bike is: Ribble Gran Fondo

I've been riding for: 10-20 years  I ride: Every day  I would class myself as: Expert

I regularly do the following types of riding: time trialling, commuting, club rides, sportives, fixed/singlespeed,


With 20 years of road cycling and over 150,000 miles in his legs it's safe to say Stu is happiest when on the bike whatever the weather. Since writing his first review for back in 2009 he has also had a career in engineering including 3D-CAD design and product development, so has a real passion for all of the latest technology coming through in the industry but is also a sucker for a classic steel frame, skinny tyres, rim brakes and a damn good paintjob.
His fascination with gravel bikes is getting out of control too!

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