Like this site? Help us to make it better.

Castelli Nano Flex 3G Knee Warmers



Dependable and comfortable knee warmers that keep in the warmth, keep out the wet and stay in place
Great fit
Stay up well throughout long rides
Warm and water repellent
No reflective elements
Marketing material says one seam, when there are clearly two...

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.

What the scores mean

Good scores are more common than bad, because fortunately good products are more common than bad.

  • Exceptional
  • Excellent
  • Very Good
  • Good
  • Quite good
  • Average
  • Not so good
  • Poor
  • Bad
  • Appalling

The Castelli Nano Flex 3G Knee Warmers are warm, comfortable and water-repellent knee warmers that work very well on the bike and have a nice mid-calf length – but they are expensive.

As you may have guessed from the name, the Castelli Nano Flex 3G Knee Warmers are essentially strips of Castelli's Nano Flex material used as knee warmers.

Castelli uses Nano Flex across a lot of its winter gear, from bib tights to gloves and beyond. In addition to being warm and fleecy, the material has been coated in nanofilaments that also make the material water-resistant. 

If you are looking for a pair of knee warmers – or arm or leg warmers – check out our best arm and leg warmers buyer's guide.

2022 Castelli Nano Flex 3G Knee Warmers - back with shorts.jpg

Nano Flex is an ideal material for knee warmers because it's quite stretchy – but it still retains the warmth and water-repellent properties you need at this time of year. A win-win-win.

I wore these in what I think it's fair to think of as 'mixed' conditions – this winter proving the perfect testing grounds for knee warmers, if not necessarily for enjoyable cycling. They kept my legs comfortable and warm throughout, and even on cold descents I never wished I was wearing anything different.

2022 Castelli Nano Flex 3G Knee Warmers - front with shorts.jpg

The material's water-repellent properties are equally impressive, and when it rains you can see the water forming into little droplets on the surface of the fabric. It's a bit like something from a mid-90s infomercial about a frying pan coating. Even when the heavens opened, these managed to keep me warm and dry.

2022 Castelli Nano Flex 3G Knee Warmers.jpg

Their breathability and wicking also seem good, the warmers quickly wicking sweat away from my skin and the material drying quickly. I find this particularly important for knee warmers, given the potential for chafing increases with damper material.

In addition to the material, these also excelled when it came to the fit.

2022 Castelli Nano Flex 3G Knee Warmers - back with shorts.jpg

They're a good length, sitting about midway down my calf, and paired with a set of winter bib shorts and long socks, they could almost be a replacement for bib tights.

2022 Castelli Nano Flex 3G Knee Warmers - cuff 2.jpg

They sat well against my skin without bunching, helped by top-and-bottom silicone grippers that stop them slipping during your pedal stroke.

2022 Castelli Nano Flex 3G Knee Warmers - cuff 1.jpg

This kind of grip helps to reduce the chances of irritation, but Castelli has also used a flatlock stitch down the inside of both seams. The seams themselves have been designed to follow the shape of your leg, with a curve towards the bottom that allows them to contour better around your knee, further reducing the chance of the material rubbing against your skin.

Somewhat oddly, Castelli claims in its marketing material that there is a single seam when there are clearly two.

2022 Castelli Nano Flex 3G Knee Warmers - logo.jpg

The knee warmers have only two bits of branding, with Castelli on one side and Nano Flex on the other.

2022 Castelli Nano Flex 3G Knee Warmers - logo 2.jpg

These seem to be well attached, which I can attest to after they were accidentally put through the tumble dryer – something that has seen the death of lots of branding on cycling kit in the past. Castelli has potentially missed a trick by not making these reflective, but it's not a game-changer.


The £50 RRP is expensive for knee warmers, but their excellent quality goes a long way towards justifying this price. The Pactimo Alpine Thermal RT Knee Warmers that Iwein reviewed are similarly priced at £53 and have some compression qualities, which the Castellis don't, but the Pactimos don't offer the same kind of coverage.

Jo tested the Kostüme Unisex Knee Warmers, which come in at £45, but found the tailoring so-so and the reverse grippers weren't as effective as some.

I was very impressed with the Castellis. Knee warmers may theoretically be such a simple piece of kit, but they're also very easy to get wrong. Castelli has clearly thought about some of the (literal) sticking points and addressed them well.

Whether it's the effective silicone grippers or the contoured seams, they are easy to just chuck on and forget about – with no mid-ride adjustments required. The material is also excellent, keeping out the wind and rain, helping to keep you warm and comfortable.


Dependable and comfortable knee warmers that keep in the warmth, keep out the wet and stay in place test report

Make and model: Castelli Nano Flex 3G Knee Warmers

Size tested: Medium

Tell us what the product is for

Nano Flex for the ultimate warmer: warm and comfortable in dry conditions, water repellent in damp conditions, and still warm in extreme conditions.

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

Water-repellent thermal and breathable Nano Flex fabric

Flat-lock stitching with single seam [it's not, there are two]

Double-sided silicone grippers to keep warmers in place

Rate the product for quality of construction:

Very well made, with strong flat-lock stitching and good choice of material.

Rate the product for performance:

They keep out the cold and wet while keeping your legs warm and toasty – a nice combo.

Rate the product for durability:

Nothing to suggest they wouldn't last – they even survived an accidental tumble dryer incident without any impact on their performance or the logos.

Rate the product for fit:

Very good fit, thanks to the stretch in the fabric combined with the contoured seams.

Rate the product for sizing:
Rate the product for weight:

As expected. It's a pair of knee warmers...

Rate the product for comfort:

They're very comfortable, with a soft fleecy inner, an excellent fit and a secure hold.

Rate the product for value:

There is no getting around the fact that these are expensive, but given their performance it is about what I'd expect.

How easy is the product to care for? How did it respond to being washed?

Easy – wash at 30°C and line dry (though I accidentally found out they'll survive at least one tumble-dry cycle).

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

Very well – they kept out the worst weather while allowing me to stay warm and comfortable on long rides.

Tell us what you particularly liked about the product

The waterproofing – there is something about seeing water bead on your knee warmers that's really satisfying.

Tell us what you particularly disliked about the product

The price – these are expensive!

How does the price compare to that of similar products in the market, including ones recently tested on

The Pactimo Alpine Thermal RT Knee Warmers that Iwein looked at are similarly priced at £53 and offer compression, which the Castelli warmers don't, but they don't offer the same kind of coverage.

Jo looked at the Kostüme Unisex Knee Warmers that come in at £45, but found the tailoring to be so-so and the reverse grippers weren't as effective as some.

Did you enjoy using the product? Yes

Would you consider buying the product? Yes

Would you recommend the product to a friend? Yes

Use this box to explain your overall score

Very good knee warmers that are a good length, offer warmth and a soft inner, while keeping out the wind and rain.

Overall rating: 8/10

About the tester

Age: 35  Height: 6 ft  Weight:

I usually ride: CAAD13  My best bike is: Cannondale Supersix Evo

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: commuting, club rides, sportives, general fitness riding, fixed/singlespeed,

George is the host of the podcast and has been writing for since 2014. He has reviewed everything from a saddle with a shark fin through to a set of glasses with a HUD and everything in between. 

Although, ironically, spending more time writing and talking about cycling than on the bike nowadays, he still manages to do a couple of decent rides every week on his ever changing number of bikes.

Add new comment


LastBoyScout | 1 year ago

I've had a pair of these (and, in fact, the full length ones) for a few years and they really are very good.

Latest Comments