Castelli Alpha Ultimate Insulated Jacket review

As the name suggests, Castelli’s Alpha Ultimate Insulated jacket is its top-of-the-range winter jacket, targeting a wide temperature spectrum from -5°C to 12°C.

This premium jacket ditches the Gore-Tex materials found on other Alpha models, instead opting for Polartec fabrics.

In testing, this winter cycling jacket has proved seriously impressive and achieves the holy trinity of being waterproof, windproof and breathable. Despite the lofty £380 ticket price, this could be the one jacket you use all winter long.

Castelli Alpha Ultimate Insulated jacket details and specifications

The Alpha range encompasses the Italian brand’s coldest-weather options, and is more heavily insulated than the Perfetto (which replaced the Gabba).

Previously, two Alpha jackets made up the range – the Alpha RoS 2 (rated between -5°C and 10°C) and Alpha RoS 2 Light (7°C to 15°C).

The Alpha Ultimate Insulated jacket is essentially a more premium offering of the Alpha RoS 2. It targets a similar, albeit slightly wider temperature range, with lighter materials.

Castelli claims the Alpha Ultimate is “30 per cent lighter, stretchier and even more comfortable to wear while retaining the same levels of warmth, breathability and protection” when compared to the Alpha RoS 2.

That’s an ambitious target and the Italian brand has achieved this with the move to Polartec.

The outer layer is constructed from Polartec’s NeoShell. Although NeoShell is claimed to be waterproof enough to keep you dry in a downpour, there’s a greater focus on breathability.

Castelli scores the waterproof ability of the Alpha Ultimate as 3 out of 5 on its own arbitrary scale, whereas the Alpha RoS 2’s Gore-Tex Infinium fabric achieves a 4.

Like the other Alpha jackets, the Ultimate has a two-layer construction with separate double-opening zips.

An equally airy Polartec Alpha layer is integrated on the inside of the jacket. As well as being breathable, it’s claimed to provide optimum insulation for its low weight.

This two-layer construction means you essentially have a jacket and thermal layer in one. You can make adjustments to the jacket depending on the temperature.

If you’re riding in wintry conditions, you can zip both layers up and pair the jacket with a long-sleeve baselayer.

Conversely, if the temperature is closer to double figures, Castelli recommends wearing a short-sleeve baselayer and keeping the Polartec Alpha layer unzipped underneath the NeoShell outer.

Outside of the Polartec fabrics, there’s “effectively waterproof” seam taping at the shoulders.

There’s also plenty of reflective detailing at the shoulders, cuffs and at the bottom of the rear of the jacket.

There are three rear pockets, with a zipped side pocket and a flat-lying hem to seal out the wind.

Castelli claims an impressive 371g weight in a size large, compared to the 525g claimed weight of an Alpha RoS 2.

The Alpha Ultimate Insulated jacket comes in three colours – Dark Grey / Black, Military Green / Black / Electric Lime and Savile Blue / Silver Reflex / Steel Blue.

The jacket is available from sizes XS to 3XL – I tested a size medium in Savile Blue.

Castelli Alpha Ultimate Insulated jacket performance

I tested Castelli’s Alpha Ultimate Insulated jacket in a variety of weather conditions, on both road and gravel. Temperatures ranged from -1°C to an unseasonably mild 13°C.

I own the current Alpha RoS 2 (and had the first-generation Alpha RoS before that). The Ultimate Insulated jacket does nothing to tarnish the Alpha name, although it’s worth bearing in mind it offers a slightly different flavour of performance compared to the Alpha RoS 2.

Most impressive is the jacket’s low weight – this is the first deep-winter jacket I’ve had where I don’t feel akin to the Tin Man from The Wizard of Oz while wearing it.

A reassuringly close fit

Castelli’s stuck with its tried-and-tested race-oriented, close-cut fit. There’s no bunching whatsoever and the sleeves are of an optimal length.

It’s worth highlighting Castelli has relaxed its sizing somewhat over the years – for comparison, my Gabba 2 high-mileage hero is an XL.

The neck of the jacket’s cut is particularly impressive and didn’t let any cold air in, meaning I didn’t need to wear a buff as I normally do.

My only qualm with the fit is that though Castelli says the sleeves have been designed to pair well with its gloves, I found it didn’t quite work as advertised during testing.

I used Castelli’s own Estremo and Spettacolo RoS gloves and found it fiddly when positioning them over the sleeves.

A wide temperature range

The jacket’s breathability is class-leading and I never felt the windchill.

I was initially sceptical about the Polartec Alpha material on the inside of the Alpha. I’ve experienced it in other jackets and oddly found it would irritate my skin for the first hour or so of a ride, despite wearing a baselayer. I’m glad to report this didn’t happen here.

Generally, the jacket seems to run a little cooler than the equivalent Alpha RoS 2. I was happy to ride with a short-sleeve baselayer until 4 or 5°C, before swapping to a long-sleeve alternative in colder conditions.

In comparison, I’m happy to wear the Alpha RoS 2 with a short-sleeve baselayer down to around 3°C.

On the two occasions I tested the jacket at -1°C, it still kept me warm enough, but it’s a shame I wasn’t able to test the -5°C claim. My hunch is the heavier Alpha RoS 2 is the better performer in the coldest conditions.

When the temperatures reached double figures, the Alpha Ultimate Insulated jacket was still comfortable to wear and I didn’t feel like I was boiling in a bag. The ability to unzip the Polartec Alpha layer helped and allowed a sufficient amount of air in.

Dark skies beckon…

The jacket is impressive in the wet, although the Polartec Neo fabric doesn’t perform as well as Gore-Tex Infinium. However, Castelli doesn’t claim it to.

One particularly memorable ride was in a snow flurry, which then turned to sleet and biblical rain. Around 10km into the 55km ride, all of my cycling attire bar the Alpha was sodden.

The jacket performed very admirably in these conditions and around two thirds of the way into the ride, I felt its tail begin to feel damp.

When I removed the jacket at the end of the ride, water had clearly started to get through the sleeves and the neck of the jacket, although my skin felt dry except at the tail.

A dropped tail (or some mudguards or fenders) could be a logical solution to this problem.

These conditions would also prove a challenge for the Gore-Tex Infinium fabric, but experience tells me I would likely be drier.

In drizzly conditions, the Alpha Ultimate Insulated jacket fended off water with ease while keeping me warm.

Like any softshell, you’ll want to protect your investment by reproofing it periodically.

Castelli Alpha Ultimate Insulated jacket bottom line

The Castelli Alpha Ultimate Insulated jacket is a fantastic winter cycling jacket and one I’ll undoubtedly be using for years to come.

Its lightweight feel and breathability are class-leading and it’ll perform very well in myriad conditions.

Castelli has done an excellent job taking what worked well with the other Alpha jackets and replicating those features using the lighter Polartec materials.

Whether or not it’s worth the £60 price hike from the Alpha RoS 2 jacket is debatable though.

It’s worth considering the type of riding and conditions you’re likely to endure if you’re stuck between which jacket to pick.