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Castelli Nanoflex Armwarmer



All the benefits of normal armwarmers with added rain resistance makes these ideal for changeable spring weather

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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These Castelli Nanoflex Armwarmer are no ordinary armwarmers. Castelli use a fabric that is treated with a with tiny silicone nanofilaments on the outside surface that means water beads off and rolls away, meaning they handle short showers and heavy downpours with aplomb, keeping arms dry in this unpredictable spring weather we're currently experiencing.

Inside is a Thermoflex fleece lining that makes them soft next to the skin but more importantly provides some thermal insulation. You can happily wear them when there's quite a chill in the air; for this reason they've been ideal for very early morning rides. Castelli quote an ideal working temperature range of 10 to 16 °C, but I've used them down to 5 or 6 °C quite comfortably. Any colder than that and I would be taking a different approach to my layering.

They're a very snug fit but not tight - typical Castelli and their racing roots - and this does mean they stay firmly in place. Some armwarmers can gradually slide down your arms during a ride, not cool, but not so with these. The tops are lined on both sides with sticky silicone gripper tape, which equally grips your skin and the jersey sleeve. They're simply constructed, with a single seam running the length of the arm, and it's hidden away on the underside of the arms.

While they're obviously very well suited to rides when you can expect the likelihood of rain, they're also very good when the forecast is a bit more positive. At this time of the year the weather can change suddenly and without much warning, and having the water resistance these provides is a real bonus over regular arm warmers. And on days when there was no chance of rain, they work just fine too, as they're very breathable so you won't overheat.

That alone makes them a very good armwarmer for this time of year and really, I can't see why you would use a regular arm warmer when you could use these. They're on the pricey side but they're a good investment in your cycling wardrobe. Put simply, they're better than all the other armwarmers out there.


All the benefits of normal armwarmers with added rain resistance makes these ideal for changeable spring weather.

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Make and model: Castelli Nanoflex Armwarmer

Size tested: n/a

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?

We always strive for total performance and total innovation, but sometimes we surprise ourselves. This Nano Flex fabric behaves just like our Thermoflex fabric in dry conditions, but then provides unbelievable water repellency when it starts raining. We don't claim that it's fully waterproof, but it's the most effective product we've ever made for keeping you comfort- able in all conditions. It's just short of a miracle.

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

Water -resistant Nanoflex fabric

Same breathability , stretch, and warmth as our standard Thermoflex warmers

Double-sided Silicone grippers keep the warmers in place

Great in every possible condition

Rate the product for quality of construction:

Tough and durable - they've stood up well to a lot of use in the time I've been testing them.

Rate the product for performance:

The water resistant treatment makes them a bonus when it rains, and they also work well when it's not raining, with good thermal insulation and breathability.

Rate the product for durability:

No frayed stitches or anything like that.

Rate the product for comfort, if applicable:

They're very comfortable once on, but they are on the snug side. That does mean they don't move about or slip down your arms during a ride though.

Rate the product for value:

As ever, there are more expensive and there are cheaper arm warmers available, but few offer the all-weather versatility these do.

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

They work like regular arm warmers in the dry, but it's when it rains they pull ahead of all other arm warmers.

Tell us what you particularly liked about the product

The fit, comfort and water resistance.

Did you enjoy using the product? Yes.

Would you consider buying the product? Yes.

Would you recommend the product to a friend? Yes.

Overall rating: 8/10

About the tester

Age: 31  Height: 180  Weight: 67

I usually ride:   My best bike is:

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: road racing, time trialling, cyclo cross, commuting, touring, mtb,


David worked on the tech team from 2012-2020. Previously he was editor of and before that staff writer at RCUK. He's a seasoned cyclist of all disciplines, from road to mountain biking, touring to cyclo-cross, he only wishes he had time to ride them all. He's mildly competitive, though he'll never admit it, and is a frequent road racer but is too lazy to do really well. He currently resides in the Cotswolds, and you can now find him over on his own YouTube channel David Arthur - Just Ride Bikes

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