Identifiable by its innovative two-layer construction, Castelli’s first Alpha Jacket was launched in 2014. Over the years, there have been tweaks to the design. In late 2025, Castelli launched the Alpha 150 jacket - available in both men’s and women’s versions - describing it as ‘the ultimate winter cycling jacket’. It's featured in our winter guides regularly over the years.
CONSTRUCTION
Castelli’s exclusive Polartec® AirCore™ fabric, used for the outer shell of the Alpha 150, is engineered for maximum air permeabilty. The electrospun membrane is designed to aid the beading of water on the fabric surface - this is a mechanical beading. A PFAS-free DWR fabric treatment adds further water repellency.
Remarkably thin for a winter jacket, and similar to many of our favourite waterproof jackets, the fabric has plenty of stretch in all directions. A two-way zip on the outer layer adds an element of self-control to the air flow reaching the jacket’s inner layer…
The sewn-in gilet, made with Polartec® Alpha insulation, is designed to provide lightweight warmth while simultaneously enhancing moisture management.
The three rear pockets are well positioned. Dropping them a few millimetres might benefit riders with less flexibility, but I’ve experienced far worse designs and never found accessing the contents too challenging.
There is a very easy-to-access zipped valuables pocket on the left-hand side. It’s brilliantly placed for fuss-free access to a house key at the end of a ride when energy levels are low. The bottom of this pocket is almost in line with the bottom of the zip, so if you forget to close it, items can easily escape - speaking from experience! On that occasion, access (infuriatingly, to my house) was anything but fuss-free.
The cuffs are a unique design. While they look sleek, I didn’t find they added any meaningful functionality. None of my gloves integrated neatly with the layering - if that’s the intention - instead sitting either fully over or fully under the cuff. After riding in heavy rain, the cuffs also remain damp post-shower, even though the rest of the jersey dries quickly.
The fit is exactly as expected. I typically wear a medium, and the medium tested fits perfectly. There’s generous length in both the arms and body, a well-considered on-bike cut, and sufficient room for a heavier base layer if needed. I’d recommend sticking with your usual size for this jacket.
The jacket is available in sizes XS through XL and comes in three colour options: Black, Hibiscus, and Bordeaux (as shown in the photos).
THE RIDE
The jacket landed on my doorstep in early January - just in time for the wettest, most miserable start to a year on record. The first few rides were in mixed conditions, with intermittent showers and temperatures hovering between 6℃/43°F and 9℃/48°F. Castelli gives a performance window of -2°C/28°F to 10°C/50°F. I’d say this is well-judged, give or take a degree or two depending on your personal internal thermostat.
From the outset, the jacket impressed, with temperature regulation really standing out. After a few tempo efforts, there were visible signs of moisture on the inside of the outer shell, yet the inner Polartec layer was bone dry - it’s a magical mid-layer.
My base layer wasn’t entirely free of dampness, but very few jackets I’ve tested manage moisture as well as the Alpha 150. The option to unzip the outer was appreciated; the inner Polartec gilet banishes the usual rush of cold air against a warm torso. The upper zipper toggle is easy to grab with gloved hands, the lower less so, but it’s still useful to let air reach the abdomen.
A brief cold snap allowed me to test the jacket in much lower temperatures - think 2℃/35°F to 5°C/41°F. For something so lightweight, it performs exceptionally well. Moisture build-up remains minimal, and there’s no noticeable chill when riding into cold winds or descending at speed. Stopping to change an inner tube on a very cold day was a breeze - no rapid cooling and subsequent shivering.
Short, very light showers were initially no problem for the jacket; water beaded and rolled off, as did road spray. Anything more prolonged dampened the outer, though the inner remained relatively dry. Thankfully, the thin outer doesn’t feel weighty when wet. It’s exceptionally fast-drying too - with the exception of the cuffs, as previously mentioned.
January’s weather deteriorated - continual rain, heavy at times. Every single ride during the second half of the month (and into February) was in the rain, on filthy roads. The outer soon stopped repelling rain, instead absorbing it from the moment the first few drops hit it. Considering the 4 out of 5 waterproof rating on Castelli’s website I was surprised how quickly performance deteriorated. With such conditions, the jacket was laundered several times a week. In short, the PFAS-free, water-soluble DWR was being exposed to far too much water - it eventually dissolved.
I’ve treated the jacket with some Nikwax spray-on reviver, it’s now repelling as well as it did on day one. In this PFAS-free era, it is impossible to buy a jacket that doesn’t need regular reviving if you ride in rainy weather. This needs highlighting on companies’ websites so that consumers aren’t misled by ratings. Nikwax’s profits should be booming. For a jacket in the price range of the Alpha 150, I think Castelli could include a free bottle of reviver upon purchase of the jacket. The need to use it will naturally correlate to how often you ride in the rain and wash the jacket.
VALUE AND CONCLUSION
With an RRP of £360/US$420, the Alpha 150 sits firmly in the ‘premium jacket bracket’. If you feel prices are getting a little out of hand, look at Q36.5’s Dottore Termica Light Mediterranea Jacket, with a comparable double-layer construction, which retails for £450/US$600. At the time of writing, the Alpha 150 is available direct from Castelli for a more palatable £252/US$294.
Other comparable options include Rapha’s Pro Team Shadow Winter Jacket at £325/US$435, though the stated temperature range is fairly conservative - -2°C/28°F to 5°C/41°F - so it arguably doesn’t represent the same level of value as Castelli’s. Assos’ Dyora R Habu Winter Jacket is another premium contender, claiming similar protection in temperatures from 2°C/26°F to 11°C/52°F, and priced at £335/US$450.
Of course, stepping away from premium brands opens up more affordable alternatives. For example, Lusso’s £160 Perform Winter Jacket, or one of Van Rysel’s winter jackets options which all come in under £80.
Given the substantial discount available at the time of writing, the Alpha 150 stands out as strong value among premium offerings. That said, I still feel the waterproof rating is somewhat exaggerated. This is worth bearing in mind if you’re considering a purchase - it will only become a concern if you regularly ride in sustained rain. In such conditions, I’d recommend adding a fully waterproof outer layer, along with a suitable reproofing treatment such as Nikwax (no doubt other brands will follow, if they haven’t already).
