The Castelli Alpha RoS 2 jacket is right at the cutting edge of winter cycling apparel and comfortable at a wide range of temperatures, but there might be a better option depending on the severity of your winter
Warm in all conditions
Clever collar and cuff
Loose neck and shoulders could be better fitted
Zippers aren't cam locked
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The Castelli Alpha RoS 2 is the brand's deep-winter cycling jacket, designed to offer comfort to those riders who will be heading out no matter what bad news the weather app has in store. It's a widely accepted opinion that Castelli makes some of the best winter cycling jackets available and, the Alpha RoS 2 is no exception. In fact, if I had to choose just one winter cycling jacket to own, the Alpha RoS 2 would be it, and that fact alone makes the premium price tag a little easier to swallow. But that's not the end of the review because, depending on where you live, Castelli's other Alpha RoS 2 Light might just be the better choice.
According to Castelli, the RoS 2 jacket is designed for use between minus five and 10 degrees Celsius (23 - 50 Fahrenheit). For anyone living in slightly milder conditions, Castelli also makes the Alpha RoS 2 Light, which is functionally similar, but suitable for conditions ranging from seven to 15 Celsius (45 - 59F).
As denoted by the 'Alpha' construction, the Alpha RoS 2 features two weather-beating layers. The inner layer is secured via two vertical seams at the rear and over the shoulders, leaving the rest of this fleecy body warmer suspended free from the outer layer.
The two layers mean there are two zippers to contend with. Neither of them are cam-locked, so you can't just flip it and tug at your collar to open it up, but the small Castelli-branded string makes it easy to grab in even the fattest of gloves. The weatherproof cover that hides the zip finishes approximately two inches from the bottom, which is a super neat design idea that makes zipping up that little bit easier whilst still moving. It's bad enough asking the group ride to stop so you can zip up your jacket, but even worse having to ride no-handed to fight your zip into place while riding in crosswinds wearing fat gloves. You might be wondering why you'd ever be unzipped but, with the two-layer system, it's possible to open up the outer layer while climbing to expel the built-up moisture and still remain comfortable thanks to the inner layer.
The internal layer is made using what Castelli calls a 3D insulation-layer fabric. The inner face of this is finished with a square mesh type design that is soft to the touch and does a sterling job of trapping warm air without becoming too warm at the higher end of the aforementioned temperature range. The outer layer is made using Goretex Infinium Windstopper, which does an equally good job of repelling wind and rain. Most of the seams on the outer layer are placed strategically out of harm's way, but those that feature across the shoulders are taped in contrasting colours for design.
At the rear, the usual assortment of three pockets each feature a trio of water drainage holes. There is also a neat security pocket over the left hip, which is well protected from the outside with a waterproof zip and Infinium material, but only mesh separates the contents from your skin/base layer, so worth considering if you were planning on storing your keys or multi-tool here. The dropped tail is held in place using a really tacky silicone strip, as well as a Castelli logo made from the same tacky finish, and this does a great job of keeping even fully-loaded pockets where they should be.
Up top, the collar is shaped to be higher at the front without bunching up at the rear, where a separate fleece layer is used to add warmth. Across the shoulder blades, two overlaid flaps are positioned to allow heat to escape without water ingress.
The cuffs are double layered and they extend well beyond the wrist, meaning they mesh well with any of the best cycling gloves with a double overlap, preventing any airflow entering up your sleeves.
Design and aesthetics
The Alpha RoS 2 comes in a choice of five colours: There's 'dark grey', which comes with light blue detailing; 'light black'; 'savile blue' with red details (tested); pro red with orange detailing; and finally 'fiery red' with electric blue details.
The lower portion, underarms and sides for all five colours are black, meaning the advertised colour is only present on the front, rear and outer half of each arm. All designs feature the famous Castelli scorpion emblem on the upper arms and the middle of the dropped tail at the rear.
The interior is given a contrasting colour, which is red in the case of the 'savile blue' jacket we have here.
I've been using the Alpha RoS 2 jacket since the beginning of winter, and while the majority of this time has been mild and wet, the past few weeks have been particularly cold, allowing me to put the temperature range to the test and I'm suitably impressed. Wearing this jacket I've experienced temperatures as low as -4C/25F, at this temperature, I paired it with a Castelli Flanders base layer, Perfetto gloves and remained comfortable and warm on a low-effort ride. For more mild days at around 4C/39F, I've paired the jacket with a short sleeve mesh base layer and remained equally comfortable.
Temperatures have yet to hit -5C/23F, but with the level of comfort I've experienced in the few degrees above, and having ridden the Alpha RoS 2 Light jacket (which is recommended down to 7C/45F) comfortably down to freezing, I feel confident that the Alpha RoS 2 can handle even cooler days than Castelli claims.
My one minor bugbear is that the fit varies from the lower body to the upper. It is particularly tight at the waist while being loose at the shoulders. It's clear to see Castelli's intention for this is to allow for movement of the upper body and protection at the core, however, for me at least, the upper body fit is too loose. This extends to the chest and upper arms, which isn't an issue, but the collar can allow a bit of wind in. Of course, there's an obvious solution of wearing a Buff, which is almost a default on the days where it's cold enough to be an issue.
In terms of waterproofing, Castelli is quite honest with its assessment, calling it 'essentially waterproof', and stating "It doesn't mean that no drop will ever come in, but we do longish rides in real rain and stay completely dry."
This is a fair assessment, and since the jacket's arrival in November, the total number of occasions where I've been soaked through equals zero, however for the days where it's guaranteed rain door to door, I've been sensible enough to pair it with a Shakedry.
On the days where I haven't, rain beads off quickly, even after two months of use and various trips through the washing machine, which is more than can be said for a lot of winter cycling clothing. In terms of care, the typical rules of machine wash at 30 apply, avoiding the fabric softener to protect the DWR coating.
There's no denying that at £290, this jacket is right at the top end of the price spectrum but, having tested it over a period of three months in varying conditions, I'm a long way to being convinced that it's worth the price tag. Of course, as you'd hope for a jacket of this price, the performance has been exemplary and with a varied choice of base layers beneath, the versatility has been excellent.
As I previously mentioned, if I had to choose just one jacket for winter, this would be it. The Castelli Alpha RoS 2 is at the cutting edge of what winter cycling jackets can achieve and with this jacket on my shoulders, I can trust that I would never be forced to turn home, no matter what winter had to throw my way. It's versatile enough in its temperature range that it will undoubtedly see you comfortably through any cyclist's typical winter. And I say 'cyclist's typical winter' because while Canadians might baulk at the British-winter temperature lows, I predict there'll be other things (like icy roads and frozen toes) keeping you from heading out the door before the jacket starts to falter.
However, I can't leave it there without mentioning the Alpha RoS 2 Light, which I've also spent the past three months testing. Depending on the choice of base layer, the Light is comfortable down to freezing and up to around 15C/59F. So while this doesn't cover the winter temperature extremes, it does equate to three-season versatility for a lot of us. So the question remains, what does your winter look like, and do you ride when the roads turn to ice? If so, the Alpha RoS is the best jacket I've ever tested in this regard, however, if you choose to avoid the coldest of days in favour of a ride indoors, then the warm-weather-friendly Alpha Ros 2 Light is likely to be the better choice.
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As the Tech Editor here at Cyclingnews, Josh leads on content relating to all-things tech, including bikes, kit and components in order to cover product launches and curate our world-class buying guides, reviews and deals. Alongside this, his love for WorldTour racing and eagle eyes mean he's often breaking tech stories from the pro peloton too.
On the bike, 30-year-old Josh has been riding and racing since his early teens. He started out racing cross country when 26-inch wheels and triple chainsets were still mainstream, but he found favour in road racing in his early 20s and has never looked back. He's always training for the next big event and is keen to get his hands on the newest tech to help. He enjoys a good long ride on road or gravel, but he's most alive when he's elbow-to-elbow in a local criterium.
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