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Castelli Nanoflex 2 Bib Shorts


Item # CST008X

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  • Black, S ($99.95)
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  • Black, XXL ($99.95)
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Item # CST008X

Keep the chamois dry.

The insulating warmth and water repellent attributes of Castelli's Nanoflex 2 Bib Shorts are the ideal match for any of the new breed of windproof, rain-resistant super jerseys based on the now-legendary Gabba. Whether worn alone for a bit of fall insulation or to make rainy spring racing endurable or matched with a complementary pair of Nanoflex leg warmers for winter base miles, the Nanoflex Bibs are among the most versatile kit that we own. They don't quite have the second-skin fit of bibs like the Free Aero Race shorts, but the benefits of a dry chamois over the course of a wet ride are impossible to overstate.

The secret to the Nanoflex 2 Bib Shorts' success is hidden subtly in their name. They're made from Castelli's Nanoflex fabric, which is a water-resistant version of Castelli's insulating Thermoflex fabric. Nanoflex is coated with millions of nanofilaments to create a water-repellant surface, compelling rain and road spray to bead up and roll off the surface. Of course, the introduction of those nanofilaments doesn't interfere with Nanoflex's thermal properties, and the brushed interior not only keeps warmth in, but it also wicks moisture away from your skin. The Nanoflex Bib Shorts keep you dry from inside and out, because nothing puts the stop to a cool, damp base mile session faster than the accumulation of clammy moisture on your skin.

The bib straps are made from breathable mesh that won't interfere with your upper-body layering with patches of extra insulation, and compressive, gripping bands at the leg openings maintain water-repelling coverage. The inclusion of Castelli's Kiss Air insert ensures a comfortable cyclist-to-saddle interface with a varying topography of breathable padding and a soft, bacteriostatic cover.

Tech Specs

Kiss Air
yes, mesh
Leg Gripper:
Claimed Weight:
[size large] 191 g
Recommended Use:
Manufacturer Warranty:
1 year

Size chart


Men's Apparel
Chest 36.2in
Waist 31.5in
Hip 37in
Inseam 31.9in
How to Measure:
For best results, take measurements over your underwear.
Measure under your arms, around the fullest part of your chest.
Measure around your natural waistline, keeping the tape a bit loose.
Measure around the fullest part of your body at the top of your legs.
Using pants that fit well, measure the crotch seam to the bottom of the leg.

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Near-Perfect Cool Weather Bibs

  • Familiarity: I've used it several times
  • Fit: True to size

I road these in several recent 70-90mi. days with 40-50deg. temps and some rain.

They are nearly perfect except for one issue: the seam across the back/bottom of the shorts crosses right where my sit bones contact the saddle. During some of the riding I didn't notice it while at other times I kept thinking that it could be causing some irritation. However at the end of each day's ride I did not have any added saddle soreness. Hopefully the thickness & softness of the Nanoflex material along with the thickly-padded chamois will make this seam a non-issue over the long run. However, it's location did unfortunately put a bug in my head about the possible source of some added butt discomfort...and we all know that this is an unwanted distraction when you're suffering. Castelli may have a reason for putting the seam there (perhaps to "shield" it from rear wheel water spray?); however, I'd happily trade this little bit of ultimate water resistance for not having a seam located in perhaps the worst possible location.

Now for what's great about these shorts:
1) Fit - They fit great like all other Castelli shorts I've owned or tried on which means they're sized for a lean, biker's body. So for me the fit is "true to size" while most other brands run large. The thicker yet-still-very-stretchy material makes them harder to put on vs. a summer-weight short, but while riding they feel like a "normal" race-cut bib to me (i.e., compressive/conforming but not overly tight or restricting).
2) Length - These are longer than your typical summer-weight short, which for me meant they come down to the top of my knee caps. I found this length to be great since I will generally be wearing knee warmers under them (i.e., the added length keeps the knee warmers in place better and allows the knee warmers to be pulled further down if needed).
3) The upgraded Kiss Air chamois seems to work nearly as well as the Progetto X2 (which is one of my 2-3 favorite chamois's). The cushion at my sit bones feels a bit less isolating due to the lack of the Progetto X2's gel inserts. However, I'd still consider it to be as good as or even superior to many other brand's top-end chamois's, which makes it a steal at this price point (so much so that my next summer-weight bib purchase will probably be a lower-end Castelli with the Kiss Air chamois).
4) Warmth - Definitely provides the added warmth in 40-50deg. weather that I was seeking vs. my summer-weight bibs (and I generally don't ride in temps lower than that).
5) Water-Resistance - Definitely fends off light rain and road spray. However I chose to wear rain pants over them during periods of heavy rain (for me the possibility of riding with a wet chamois isn't worth it just for the sake of seeing how water resistant this shorts are).
6) Miscellaneous - The Giro3 leg grippers have worked great for me in the past and so far these do too given that they're tighter than on a summer-weight short (i.e., since they are gripping the narrowest part of my thigh just above the knee). Finally I might complain about the bunchy traditional seamed-mesh bib straps but at this price it's hard to expect much more (and I'll generally be wearing them over an undershirt such that this issue is not really noticeable).

In conclusion, other than than the oddly placed rear seam, these shorts do what they claim to do (and do it better than the thermal shorts from Bontrager or P.I.). They are a steal at this price for something with the Castelli name on it. Buy 'em unless you see value in the extra cash needed for the likes of the Assos or Rapha thermal bib shorts.


  • Familiarity: I've put it through the wringer
  • Fit: Runs small
  • Size Bought: XXL

These are the cold-weather cycling equivalent of a good sourdough starter. I wear them in the high 50s, add knee warmers down to the low 40s, and supplement with a pair of thermal tights over the top in the 30s. Anything colder than 30, and I stay inside and drink whiskey.

The water resistance hasn't faded over a dozen+ washes. While Nanoflex won't keep you dry in a deluge or if you jump into a pool, the material does the trick in sprinkly conditions or if the road's damp. I opted for a slightly more accommodating fit with XXL rather than risk a see-through ass panel on the XL. You're welcome.

Great shorts!

  • Familiarity: I've put it through the wringer
  • Fit: Runs small
  • Size Bought: Large

The shorts provide a lot of extra warmth when the weather gets down into the mid 30s. I have used them with legwarmers down to the mid 30s easily . In cooler weather, or use a heavier tight with these and stay very warm. They are pretty snug, but they xdo not ride up When you're wearing them with tights.

What makes these different to the nanoflex 1 shorts?

Best Answer

The only thing I can see just from reading the product description is nanoflex is a Kiss 3 and the nanoflex 2 is a Kiss Air chamois.