It's usually hard to get overly excited about arm warmers. After all, how much can you do with a Lycra tube? But Castelli's Thermoflex are the exception. Their advantages are individually small, but they all add up to create one of the most comfortable, best fitting sleeves on the market.
The Thermoflex name comes from the fabric. It's fleece lined to trap a layer of warm air against the skin which it does well providing plenty of warmth in temperatures ranging from mid-single figures to the low teens. In fact Castelli recommend 5 - 15°C so it safe to say they've got that right.
It's a medium weight material that breathes pretty well too although once you push on a bit on warmer days your arms will get a bit clammy. If you have to stop though your damp arms don't get cold.
The best thing about the Thermoflex Arm Warmer, though, is the fit. They are anatomically shaped during construction; a pre bent elbow if you like. The Thermoflex material is super stretchy so it fits closely and moves with your arm. This means there are no creases or rucks in the material, better for comfort and aerodynamics.
To keep things in place Castelli use silicone grips top and bottom, nothing new there admittedly but a neat addition is the silicone grip on the outside at the top to grip your jersey sleeve. No more of that unacceptable strip of flesh between sleeve and warmer. Things don't move at the wrist either, even if you've stretched the arm warmers a long way. Wherever everything sits at the start of a ride is where it'll be at the end.
Castelli seem to have adopted three staple colourways for all of their kit this year and the Thermoflex range is designed to match. You can still get your regulation black but you can also get it with a fluoro yellow or red cuff stripe. It's just on the one sleeve though, which might be a bit Rapha-esque for some maybe. There is also a white/red version. Sizing goes from small through to extra large with us trying the medium which fitted my pathetic 33cm diameter cyclist biceps.
Overall the Thermoflex are the best arm warmers in my wardrobe thanks to the great fit which stays put no matter what. Their only rival is a pair of Castilli Nano-Flex warmers which are basically Thermoflex with a water resistant coating. Temperature regulation is good as is breathability which makes them very comfortable to wear for long periods of time. In fact I don't think I've worn a long sleeve jersey for the last month.
Quality is excellent even by Castelli's standard and these are definitely worth the 25 quid retail price, although as with anything you can get them cheaper on line.
A lot of neat little touches backed up with quality and stylish looks, super cool & super warm
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road.cc test report
Make and model: Castelli Thermoflex arm warmer
Size tested: S, M, L
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?
These are Castelli's mid-weight arm warmers designed for use between 5-15 degrees C. They have a performance orientated fit as you'd expect from Castelli.
Tell us some more about the technical aspects of the product?
*Thermoflex fabric for soft, warm, stretchy comfort
*Microfibre gripper elastic at top
*Sublimated Castelli wordmark
*Size range S-XL
Tell us how the product performed overall when used for its designed purpose
Brilliantly, they perform as they should backed up by a brilliant fit.
Tell us what you particularly liked about the product
The fit and smart styling.
Tell us what you particularly disliked about the product
nothings perfect but there is very little to dislike.
Did you enjoy using the product? Yes.
Would you consider buying the product? Yes.
Would you recommend the product to a friend? Yes.
About the tester
Age: 35 Height: 180cm Weight: 76kg
I usually ride: Whatever needs testing or Genesis Flyer, fixed of course! My best bike is: Kinesis T2 with full Centaur Red
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 road.cc 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!