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Castelli Nanoflex kneewarmers



Great wet weather performance and wonderfully warm but the seam placement could irritate.

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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Castelli Nanoflex kneewarmers combine two handy functions, keeping your knees both warm and dry. Their only downside is a slightly awkward seam.

Castelli's Nanoflex is a water repellent range of garments based on their Thermaflex material but with silicone filaments added to the surface. These filaments are what keeps the rain out, causing it to bead on the surface and be moved away by the wind.

Heavy drizzle, road spray and riding through fog have little impact on these knee warmers and you'll remain dry for a very long time. Eventually the wet will break through as the fabric gets overwhelmed but it'll take a good soaking before that happens.

Unlike waterproofing treatments the silicone filaments aren't washed away in the washing machine. They are attached to the surface and are part of the material so the performance throughout their life should remain a constant. The care instructions recommend a cool 30 degree wash and not to tumble dry as the silicone isn't a fan of too much heat.

Right then, we've established they'll keep you dry but are the Nanoflex knee warmers worth paying thirty five quid for?

They're Castelli so that does carry a bit of a premium but thankfully they do have the performance to back that up. The fit is very good with a large size staying put on my 55cm upper thigh, a silicone gripper holding the top in place while elastic takes care of the bottom.

The inner is a fleecy lining Roubaix style that is very soft to the touch and keeps your knees warm even when the rain eventually gets through. The Thermaflex fabric does exactly what the title suggests, flexes and moves with your leg while travelling through the pedalling motion.

One whinge though is the seam that runs up the rear. On rides over a couple of hours the seam would start to rub the skin on the back of my knee, which was quite irritating. They aren't articulated at the back of the knee either which does cause the seam to bunch.

Manufacturing wise it's all good. The stitching is good quality and after plenty of wear and machine washes there is no sign of an fraying.

There are three colours available, red, white and black, in sizes from small to extra large.

So are they worth £35? Yes I reckon they are provided that seam doesn't annoy you.


Great wet weather performance and wonderfully warm but the seam placement could irritate.

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Make and model: Castelli Nanoflex Kneewarmer

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?

Pro performance knee warmers aimed at riders who train in all weathers. The fit is good and stretches with the constant pedalling motion.

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

Silicone nano filaments cause water to bead off of the surface to create a water repellent material.

Rate the product for quality of construction:
Rate the product for performance:
Rate the product for durability:
Rate the product for comfort, if applicable:
Rate the product for value:

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

Performance is great and they fit well. The water repellency is impressive and they should last a good few seasons.

Tell us what you particularly liked about the product

The water repellent performance, warmth and build quality.

Tell us what you particularly disliked about the product

That irritating seam.

Did you enjoy using the product? Yes when they weren't rubbing.

Would you consider buying the product? No.

Would you recommend the product to a friend? Yes.

Anything further to say about the product in conclusion?

A glance on the forums and speaking to club mates sees the majority of users don't suffer with the seam so its probably a case of try before you buy.

If they are comfortable on you they are some of the best performing knee warmers on the market

Overall rating: 8/10

About the tester

Age: 34  Height: 180cm  Weight: 76kg

I usually ride: Ribble Winter Trainer for commuting, Genesis Flyer  My best bike is: Sarto Rovigo

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,


As part of the tech team here at F-At Digital, senior product reviewer Stu spends the majority of his time writing in-depth reviews for, and ebiketips using the knowledge gained from testing over 1,500 pieces of kit (plus 100's of bikes) since starting out as a freelancer back in 2009. After first throwing his leg over a race bike back in 2000, Stu's ridden more than 170,000 miles on road, time-trial, track, and gravel bikes, and while he's put his racing days behind him, he still likes to smash the pedals rather than take things easy. With a background in design and engineering, he has an obsession with how things are developed and manufactured, has a borderline fetish for handbuilt metal frames and finds a rim braked road bike very aesthetically pleasing!

Add new comment


laterrehaute | 8 years ago

Same seam issue.  I have moved them around so the seam is onthe inside and no problems.  Surprisingly no one has commented on the writing being at the back - I do wonder if it is more a hindrance than a benefit to car drivers at night.  Wondering if the leg warmers will have the same issue, although the reviewer does not mention it.

nowasps | 10 years ago

Just bought the Sportful Norain version of these. Same seam issue.

5th | 10 years ago

I've got the full set of these (arm, leg and knee) and think they're great, warm, fit well etc. The only problems I have are that the water repellency doesn't last (mine had a lot of use over the last winter and spring and the water doesn't bead up and run off any more) and they occasionally ride down a bit, but this is probably due to my hairy legs - a brief spell of Rule #34 compliance saw them stay in place just fine. No issues with irritating seams either. Maybe I'm just different?

kingbucko75 | 10 years ago

Goe the full length legwarmer version....the seam in those drives me crazy too but they are great at keeping the rain out. Teamed up with the matching armwarmers and Gabba jersey they are simply the best wet weather gear

pepita1 | 10 years ago

I have both the arm and knee warmers and find them fantastic for keeping rain at bay. They are highly breathable as well. I purchased mine at this year's Dartmoor Classic and was very glad I did! They stood up very well to the driving rain and wind.

You're right about the seam on the knee warmers but, for me, after about 10-15 minutes, I don't notice it anymore.

notfastenough | 10 years ago

Sounds spot-on to me, the seam is a bit odd. Somehow though, it only irritates if it's in the centre of the rear of the leg. Just a bit closer to the inside of the leg and I find it fine.

Darkerside | 10 years ago
1 like

I just shift the seam round to the inside of the leg. They don't seem particularly preshaped so there's no difference in fit.

Wore them like this for about half of the five days of LEL with no irritation.

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