Castelli Nano Flex Arm Warmers Review


Castelli’s Nano Flex fabric technology is designed to offer the warmth and comfort of their Thermoflex fabric – but with the addition of a water repellent coating. Ideal for riding in changeable weather conditions. As here in the UK, this could be any season – we’ve been testing the Castelli Nano Flex Arm Warmers.

The Technology

Castelli developed their Nano Flex fabric from the foundations of their popular Thermoflex fabric. The arm warmers are made from a Nylon/Spandex mix which makes them breathable and extra stretchy. Whilst a brushed fleece lining which provides both comfort and warmth. There is a silicone gripper around the top of the arms – on both the inside and outside of the arm warmer. This means that they stay up your arm and well as gripping the inside of your jersey sleeves.

Soft fleece lining for warm & double-sided gripper holds the warmers in place.

Soft fleece lining for warm & double-sided gripper holds the warmers in place.

What makes the Castelli Nano Flex arm warmers an advancement on the Thermoflex though, is their water repellent abilities. The Thermoflex fabric is treated with millions of tiny (silicone) nanofilaments. This coating provides a barrier to help prevent water soaking through the fabric. Nano Flex is not completely waterproof and if you are riding in heavy rain showers, you are likely to get wet. However the coating means that light rain or spray from wet roads – beads on the surface of the arm warmers and runs off.

Castelli Nano Flex Arm Warmers

Whilst not fully waterproof – light rain and spray stays on the surface.

In Use

Arm warmers are arguably one of the main clothing accessories found in most riders kit drawers. They are designed to be easy enough to put on and take off, mid-ride. They can be rolled up small enough to be carried in a jersey pocket when not in use and thanks to technical fabrics like Nano Flex, they can even keep you dry(ish). I have been using the Castelli Nano Flex arm warmers for a while to give them a fair test. To be honest, it was more a case of finding a dry day to test them on. The brushed fleece lining is very soft and comfortable and provide excellent insulation on colder rides. That being said, these arm warmers are nicely breathable when the body temperature increases. The outside of the fabric is more course thanks to the nano-filament coating – but is still very stretchy thank to the Nylon and Spandex mix. The Castelli Nano Flex arm warmers feature a logo that you can’t really miss on the lower arm. This is simple, white (or black on the white arm warmers) and not reflective. In fact, there is no reflective detail on these arm warmers. I really like the double-sided silicone gripper around the top of the arm. It does a great job of not only preventing the warmers from sliding down the arm, but also prevents the jersey sleeves from riding up. This helps to prevent that annoying gap between sleeves that are slightly too short and the top of the arm warmer.

Castelli Nano Flex Arm Warmers

Hard to miss logo is disappointingly large with no reflective detail.

Sizing the Nano Flex arm warmers is a little awkward. Sizes range from S-XL and Castelli’s size guide for warmers is based on rider weight. This means that for me weighing over 90kg, I needed an XL. However, the XL size I tested were really too long. I am not sure if a large would have fitted better, but I feel that sizing by height may be a little more accurate.


Castelli Nano Flex Arm Warmers review conclusion

There is no doubt in my mind that the Castelli Nano Flex arm warmers are very good. They provide excellent protection against the cold and (light) rain. Even getting caught out in a downpour, they won’t keep you dry (remember they are not waterproof) but the arm warmers remained very comfortable. This is important in a category where they are up against some strong competition from the likes of Sportful and dhb. The double-sided gripper at the top of the arm is a nice feature and works very well. The large logo on the forearm won’t be to everyone’s taste and I think that the fact it is not reflective is a missed opportunity. The lack of any reflective detail is disappointing as I think that it is an important feature for many recreational riders. The Nano Flex arm warmers are available in 3 colours – black, white or red and sizes range from S-XL. Pricing wise, the Castelli Nano Flex retail at around £28 but at the time of this review, you can find discounts of around 20-25% from the likes of Wiggle and Chain Reaction Cycles.


8.8 Very Good

Going by the size guide, the Nano Flex arm warmers seem to come up a little on the long side. However, they are warm, breathable and brilliantly water repellent.

  • Fit 8
  • Design 9
  • Performance 10
  • Value 8

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