Arm warmers are an essential take-along this time of year. You either wear them all ride or stash them in a jersey pocket for chilly descents. When it comes to foul weather protection, few compare to the Castelli NanoFlex arm warmers.

Castelli NanoFlex Arm Warmers Features:

  • Water-resistant NanoFlex fabric
  • Same breathability, stretch, and warmth as standard Thermoflex warmers
  • Double-sided silicone grippers keep the warmers in place
  • Fleece backing increases warmth and next-to-skin feel
  • Colors: White, Red or Black
  • MSRP: $69.99

Castelli NanoFlex Arm Warmers in the Rain

My NanoFlex Experience

Over the years, I’ve been impressed with Castelli’s products and the NanoFlex Arm Warmers are no exception. You’d think something as simple as arm warmers would be a piece of cake to make, but there are so many variations in arm warmers that these will certainly find their place in the pack.

The star of the show is the NanoFlex fabric. This stretchy, fleece-backed fabric is really Castelli’s Thermoflex fabric that’s been treated with nanofilaments of silicone fiber. That treatment turns these arm warmers into a nearly-impermeable weather barrier. Castelli calls it highly water resistant, but in my rain testing, I found it about as waterproof as it gets. Check out the water beading up.

Like any fabric coating, enough moisture will overwhelm it and that will most certainly be the case with these. But, the Thermoflex fabric will also do a great job at maintaining warmth when wet.

I tested the size Large and found them to provide wrist-to-armpit coverage. Funny, I’ve never measured my arm length, but these warmers come in at 19.5″ in length and do indeed cover the entire length of my arm with the silicone-backed upper cuff sitting at my armpit. This full coverage makes up for any gaps between a vest (like the Castelli Fawesome) and the arm warmers for a functional weather barrier.

Castelli NanoFlex Arm Warmers & Fawesome Vest in the Rain

Slipping them on is best done by first wrapping the upper cuff over itself so the silicone doesn’t grab your arm hairs. Once you do that, they can easily slide over bracelets (like my Road ID slim) and watches (even the bulky Suunto Ambit 2s). While they aren’t articulated at the elbows, the stretchy fabric fits well — though the fabric does bunch up a bit on the inside of the elbows. The double-silicone upper cuffs keep both the warmers and your jersey in place. I’ve worn them with a variety of jersey fabrics and the silicone grips all types.

Aside from the lack of articulation, the full-length seam could be irritating for some. Perhaps the fabric doesn’t take a flatlock seam very well or something, but I’d put it on my wishlist. I wore these in cool rain (upper 50’s) and on a couple of cold, dry mornings in the mid 40’s. I noticed the chill once temps were in the solid 40’s, but that’s about when you’d be opting for a thicker shell over arm warmers anyway.

The Good:

  • Soft next-to skin
  • Grippy material on inside/outside of upper cuff keeps ’em in place
  • Sheds water aplenty
  • Excellent wind protection
  • Still remain breathable

The Bad:

  • Full-length seam can be irritating
  • No elbow articulation, so they bunch up
  • Inner silicone does pull on armpit hair

The Bottom Line

Pro teams and all-weather riders alike can appreciate the weatherproof barrier provided by the Castelli NanoFlex arm warmers. They shed water with ease and provide warmth in the temps you’d expect. They are a little more expensive, but if weather protection is what you need, take a look at these.

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About Author

A native of the Pacific Northwest, Jason quickly developed a love for the outdoors and a thing for mountains. That infatuation continues as he founded this site in 1999 -- sharing his love of road biking, mountain biking, trail running and skiing. That passion is channeled into every article or gear review he writes. Utah's Wasatch Mountains are his playground.

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