Castelli offers a trio of winter options in its highest performance Rosso Corsa product line. Being a Rosso Corsa product means the best quality chamois and the Nano Flex Pro 2 bib tight is the option aimed at wet and cold, but not sub-zero, winters. If that’s what you need, these could be enough to get you through the winter.
Pros
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Large area of high reflectivity at both ankles
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Limited seams
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Progetto X2 Air Chamois
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Rubberised sewn-on logo will not peel and crack
Cons
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Short leg length makes sealing at ankles more difficult
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Low in the abdomen
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Castelli makes a winter bib tight for every situation, and while there’s a lot of overlap, they each have their unique set of features. You could get away with using any of them for most winter situations but it also makes sense to choose the option that fits your needs best. Our list of the best winter bib tights for cycling in the cold highlights a couple of the most well-rounded options. For those that want to specialise a bit more, that means looking outside of the list.
If cold and dry weather is what your winter looks like then the Sorpasso RoS Wind bib tight is the option that makes more sense. If you've got a winter that looks just a little warmer and quite a bit wetter then that means you are going to need a different option. Castelli thinks that might be the Nano Flex Pro 2 bib tight so we put them to the test on the bike. If that sounds like it might match your winter needs, keep reading to see what we think.
An extra panel at the rear helps mitigate a soaked chamois from road spray. (Image credit: Josh Ross)
Design and aesthetics
No matter what piece of clothing you are looking at, if it's Castelli and it carries the Rosso Corsa tag then it's the highest quality that the brand makes. More than even being of the highest quality, the designation means it is the most performance-oriented. The fit will be tighter, the technology higher, and aerodynamics are front and centre.
If it's a bib tight, like the Nano Flex Pro 2, then Rosso Corsa also comes with the Progetto X2 Air chamois instead of the KISS Air 2 pad that you'll find lower down the model line. The KISS Air 2 is a high-quality option but the Progetto X2 Air takes things a bit further, including a floating design instead of an attached foam design.
Castelli isn't alone in using this strategy of a floating chamois. The idea is that as the outer layer moves, there's some ability for the inner layers to remain connected to your body, however, the biggest change isn't actually that movement. Under each sit bone and the perineum is a viscous (consider it a gel) padding. Although it's undetectable as anything separate, it can't be fully compressed.
The size of the two pads is a bit different as well. The KISS Air 2 is a little bit bigger so as to better handle upright riding positions, while the Progetto X2 Air assumes a more aggressive riding position and so covers a smaller area. It's not a huge change but you might notice it depending on the riding you are doing.
The slight colour change shows the area of double thick rain-shedding material. You might also notice that Castelli has finally updated its logo to a three-dimensional version that will not crack and peel off. (Image credit: Josh Ross)
With the Nano Flex Pro 2 being part of the Rosso Corsa lineup, that puts it into the same range as the Sorpasso RoS and the Sorpasso RoS Wind bib tight. The first of those is the most well rounded, the second is specifically designed for cold and dry weather, and the Nano Flex Pro 2 is the option for cold and wet.
With that focus in mind, the first change is with the use of a different fabric. While the Sorpasso RoS options use Nano Flex 3G, like the arm warmers with the same name, the Nano Flex Pro 2 bib tights move to the Nano Flex Xtra Dry fabric. It still uses the same combination of DWR (durable water repellent) coating coupled with "millions of ultra-tiny nanofilaments" but the outer face is different. Nano Flex Xtra Dry has a double-face knit that results in a smoother, tighter, more weather-resistant design.
To support the new fabric, there are also some design changes. Given that water ingress is most likely at the seams, Castelli has limited the number of seams in the Nano Flex Pro 2 bib tight. While the Sorpasso RoS patterns use complicated patterning and different fabrics, the Nano Flex 2 uses a single piece of fabric for each leg. There are no seams across the legs horizontally and just a single seam starts at the bottom and holds to the outer edge before curving behind.
In areas where even the impressive Nano Flex Xtra dry isn't enough, Castelli has used a couple more tricks. On the bottom, inner, of each leg there's a rubberised panel that's both reflective and entirely waterproof. It sits over the top of the Nano Flex Xtra dry so while it's not breathable there's no rubberised against the skin feel. Then on the low back instead of anything completely waterproof, there's a double layer of the Xtra dry fabric. These are the areas that are most likely to experience road spray so they get a bit of extra protection.
The inside of each leg has a layer of waterproof and rubberised fabric that's highly reflective. (Image credit: Josh Ross)
Performance
In the early autumn, I rode with a friend who had these on. It was his feeling that they were enough for the winters in this area of the world - Portland, Oregon - and I was pretty sure they weren't. After riding through the winter's worst, I'd say the answer is that he was probably right, kind of.
These are the Castelli answer to cold and wet riding but for those who ride in British or Pacific Northwest rain, these aren't enough. At least not for rides that last 6-7 hours, although I accept that's a pretty extreme request for any garment. If your rides are shorter, or less rainy, you might be able to get away with just the Nano Flex Pro 2 bib tights. What I can say is that if any softshell bib tight solution was going to work on a rainy ride, this Castelli option would be it.
Wet weather performance is only one aspect of winter riding though. When you look at cold-weather performance, these don't quite match the performance of the Sorpasso RoS Wind bib tights. While those would let you dip down below freezing, you are going to want to keep these for slightly warmer weather. The official Castelli range given is -2C/28F to 10C/50F but I'd recommend keeping your lowest temps to around 2C/35F and only when you expect it to warm up. They really start to feel good around 4.5C/40F and the upper range of 10C/50F does hold true.
Looking back at the discussion I had at the beginning of the winter, I do think you could make it through if these were your only bib tights. Leaving the house when it's 2C/35F you'll feel cold, but the tight outer knit does a pretty good job of handling the air movement as you start riding, so you won't get colder covering ground in the flats in low wind situations. You won't be feeling especially warm, but as the day warms up just a little, you will start to feel comfortable and if you get some light rain, you won't have to worry since the water resistance will do a good job in all but the most sustained rain. If you want to handle colder, rainier, longer rides then add a pair of hardshell trousers, or conversely, if you’ve got weather like much of the Southern United States, these might even be warmer than you need on their own.
Nano Flex Xtra dry has a tighter weave on the outer face but the inside is the same super comfortable fleece as the Nano Flex 3G Castelli uses elsewhere. (Image credit: Josh Ross)
Verdict
It's not always easy to work out exactly what every overlapping option in the Castelli lineup is best for, but the Castelli Nano Flex Pro 2 is for cold, wet, winter riding. In that respect, it lives up to its marketing and beyond that, it's got one of the best chamois inserts on the market and it's comfortable in the knees.
When it comes to negatives, the biggest issue is unlikely to be an issue for most people. Despite the zippered ankle, there's not a lot of room to get the ankle over the top of bulky boots, so these are going to pair best with something from our list of the best cycling overshoes and slimmer road shoes. At the other end of the design, I'd love to see just a little more height on the torso.
For British (or the American Pacific Northwest) winters, the Castelli Nano Flex Pro 2 could be enough to get you through if it's all you own, but there will be days when you are on the performance edge and may be left wanting more.
Josh hails from the Pacific Northwest of the United States but would prefer riding through the desert than the rain. He will happily talk for hours about the minutiae of cycling tech but also has an understanding that most people just want things to work. He is a road cyclist at heart and doesn't care much if those roads are paved, dirt, or digital. Although he rarely races, if you ask him to ride from sunrise to sunset the answer will be yes.
Height: 5'9"
Weight: 140 lb.
Rides: Salsa Warbird, Cannondale CAAD9, Enve Melee, Look 795 Blade RS, Priority Continuum Onyx
