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Castelli Alpha Ultimate Insulated Jacket review

The halo Alpha jacket is mostly a delight 

Our rating 
4.5 out of 5 star rating 4.5
GBP £380.00 RRP | USD $449.99 | EUR €349.95 | AUD $600.00
Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket

Our review

A seriously impressive winter jacket without the bulky weight 
Pros: Exceptional fit; impressively light; breathable; good waterproofing; stylish; excellent wind protection 
Cons: High price; not quite as warm as claimed in cooler temperatures; no dropped tail 
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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.

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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

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
The Alpha Ultimate Insulated jacket costs a heady £380 / $449.95 / €349.95.
Gary Walker / Our Media

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.

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
The Polartec Neoshell outer shields you from the wind and rain.
Gary Walker / Our Media

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.

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
The Polartec Alpha layer on the inside keeps you warm.
Nick Clark / Our Media

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.

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
There are three rear pockets and a zipped security pocket.
Nick Clark / Our Media

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

Oscar Huckle riding Niner RLT 9 RDO with Castelli Alpha Ultimate Insulated Jacket
Yes, I even took the jacket through a river crossing.
Robert O'Keefe / Our Media

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

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
A close fit at the neck means you shouldn’t need to wear a buff.
Nick Clark / Our Media

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.

Castelli Estremo gloves being worn over Castelli Alpha Ultimate Insulated Jacket
The jacket didn’t play nicely with Castelli’s own gloves.

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

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
Simply pair the jacket with a temperature-appropriate baselayer and adjust the zip on the Alpha layer…
Gary Walker / Our Media

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.

Oscar Huckle wearing Castelli Alpha RoS 2 jacket.
I’d suggest the Alpha RoS 2 is the way to go if you’re riding in the coldest of temperatures.
Oscar Huckle / Our Media

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…

Oscar Huckle wearing Castelli Alpha Ultimate Insulated jacket.
I took the jacket out in a snow flurry.
Oscar Huckle / Our Media

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.

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
A dropped tail could be the answer for seriously wet escapades.
Nick Clark / Our Media

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.

Value for money

At £380, the Alpha Ultimate Insulated jacket is one of the most expensive winter jackets on the market.

Correct me if I’m wrong, but I believe only the Assos Equipe RS Winter Jacket Johdah usurps it, retailing for a frankly upsetting £575.

While £380 is a significant amount of cash, this jacket saves the need for buying lots of layers or jerseys.

Ultimately, you just need this garment and a baselayer and you’ll be covered for most winter conditions.

Going by other Castelli jackets I’ve used in the past, it’ll likely last for years if you take good care of it.

Does the jacket justify the extra £60 over the Alpha RoS 2? That is a more difficult question, given it doesn’t protect you quite as well from the rain and generally runs a little cooler.

However, the substantial weight reduction and improved performance in warmer conditions are undeniable benefits.

Castelli Alpha Ultimate Insulated jacket bottom line

Oscar Huckle modelling Castelli Alpha Ultimate Insulated jacket
This jacket delivers and then some.
Gary Walker / Our Media

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.

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

Product Specifications


Price br_price, 5, 3, Price, AUD $600.00EUR €349.95GBP £380.00USD $449.99
Weight br_weight, 5, 6, Weight, 371g (M) – Claimed weight for size large , Array, g
What we tested br_whatWeTested, 5, 8, What we tested, M
Year br_year, 5, 9, Year, 2023
Brand br_brand, 5, 10, Brand, Castelli


Features br_Features, 11, 0, Features, Polartec Neoshell outer layer, Polartec Alpha inner
Key features br_clothingKeyFeatures, 11, 0, Key features, Thermal, water resistant and windproof
Gender br_gender, 11, 0, Gender, Men's