The Castelli Alpha RoS offers a host of clever features, such as the separation of the insulating and softshell fabrics to deliver exceptional breathability and ventilation – particularly for the level of rain protection the jacket offers. Other great details include the double cuff and collar, which both do a great job at blocking out the draughts. The Alpha RoS isn't the warmest winter jacket – I'd be feeling cold by about +3°C (38°F) – but paired with a good baselayer and it can comfortably go much lower.
Double layered main body better regulates ventilation
Double cuff plays nicely with gloves
Waterproof enough for the wet, breathable enough for the dry
Double zip makes it harder to quickly dump heat
Not as warm as some competitors
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We’ve been roundly impressed by much of Castelli’s RoS (Rain or Shine) range, the balance between breathability and waterproofing not only makes riding in the wet a more pleasant experience but also makes the pre-ride decision of the best jacket to wear much easier.
The Alpha RoS 2 Jacket slots into Castelli’s range as its cold weather option, being more heavily insulated than the Perfetto (formally Gabba) and the Alpha RoS 2 Light jackets.
The construction: Castelli Alpha RoS 2 Jacket
Gore-Tex Infinium Windstopper 150 fabric is used for the outer section of the jacket to provide isolation from the elements. Although not designed expressly to be waterproof, the fabric does offer effective rain protection, with the taping of the main seams assisting with that.
Inside the jacket, the Alpha fabric provides the insulating qualities in a double layer construction. Here, the fleecy lining is kept separate from the outer softshell, almost like a baselayer crossed with a gilet.
The idea is that this will greatly increase the ventilation and comfort of the jacket, as water vapor can very quickly and easily pass through the fleecy layer (and away from your skin) before working its way through the – still highly breathable for its waterproofness – Infinium outer layer.
This construction also opens up different temperature management systems. On a long climb in the cold, you could open up the windproof outer layer to further increase ventilation while still fending off the chills with the inner layer zipped up.
Alternatively, if you’re pushing hard and fast on the flat, you could unzip the fleecy inner layer, tuck it to either side and zip up the outer layer to block out the wind.
Doubling up is a theme that pervades the jacket. There’s a double cuff at the wrists so you don’t have to choose between layering the jacket over your gloves or tucking it into them – you can do both.
Also, against the neck, the rear section has a thicker fleecy panel to help trap in heat, but that recedes for the front making for a less restrictive fit that helps when breathing hard.
The three rear pockets don’t have a storm flap to keep water from running into them, but there are three drainage holes with reflective detailing at the bottom to stop them from starting to fill up. On the left side there’s a small-ish zipped pocket which doesn’t fit medium to large smart phones, but is good for keys and cards.
In wet conditions, the Castelli Alpha RoS 2 really stands out. Generally, the design of these jackets with their lower waterproof ratings – but much greater breathability – than a hardshell rain cape means that even if you do end up getting a little damp, you at least avoid the awful feeling of 'wetting out' from the inside.
But although a great improvement over hardshell rain capes, saturated softshells still don’t feel particularly nice against the skin. The Alpha RoS 2 with its dual layer design, however, greatly mitigates this by allowing for an air-gap between the outer layer and in the inner, fleece-y one.
The breathability benefits of this feature were still noticeable in dry conditions, but a little less marked compared to its performance in the wet. The double cuff, which we are starting to see on more winter jackets these days, resolved the conundrum of whether to put the sleeves over or under the gloves and generally made for toastier feeling hands.
While the separate layers of insulating and softshell fabrics bring palpable benefits, there were a couple of niggles to the system. The two zips, with the inner one being quite small, makes it quite difficult to immediately dump a load of heat when working hard up a steep climb – in contrast to more ‘traditional’ softshell jackets which only require a quick tug on the zipper.
With the insulation split into separate parts, there do end up being some gaps and the ones across the front of the shoulders are noticeable in colder conditions. Although Castelli rates this jacket as suitable to at low as -5°C (23°F), I got cold in as little as +3°C (38°F).
The addition of a good quality merino baselayer greatly expanded the range of temperatures I’d be happy to wear the jacket in, but it is worth noting that I was able to ride in as low as -2°C (28°F) in Assos’ Mille GT Ultraz Winter Jacket Evo – and that was without any form of baselayer.
At £300.00 / $369.99 the Castelli Alpha RoS 2 Jacket is a very expensive proposition. Even the Assos Mille GT Ultraz Winter Jacket Evo is slightly cheaper at £290.00 / $369.00. However, the Alpha RoS 2 does perform notably well in terms of its breathability and ventilation, even if it isn’t the warmest winter jacket.
The Castelli Alpha RoS delivers exceptional breathability and ventilation for a softshell jacket with this level of rain protection. The host of clever details extends to the double layer system of insulating and softshell fabric – as well as the double cuff and collar.
It’s not the warmest deep winter jacket, I'd get cold by about +3°C (38°F). That said, paired with a good baselayer and it can comfortably go much lower.
- Weight: 515g (size medium)
- Sizes: S – 3XL
- Colours: Orange, Green, Black, Blue, Red
- Contact: www.castelli-cycling.com
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