Castelli Alpha Wind Jersey FZ

Bang at the top of its range of jerseys (and priced accordingly), Castelli's Alpha Wind Jersey FZ (full zip) is designed to allow you to extend the pleasure of being able to ride in just a thermal jersey to about 10 degrees colder. It has an unusual double-front design and works really well when used over a suitable baselayer, giving adjustable protection to your torso where you need it. A baselayer is key, though – without it I found that my arms got cold.

As well as being chock-full of tech fabrics and the sort of quality detailing that, frankly, you'd expect at this sort of price, the unique selling point of the Alpha Wind Jersey (unique, that is, if we're not counting a couple of other Castelli jackets with a similar construction) is the double front.

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There are two separate layers across the front of the torso, each with its own zip. The outer, like most of the rest of the jersey, is made from a lightweight Windstopper 150, a water-resistant, windproof fabric from Gore. It's thinner and less insulating than the Windstopper X-Light Plus used in a Castelli Gabba, so to keep your core warm there's an inner layer made of Prosecco Stratus. On cold days you'd have both layers zipped up, but the idea is that if you're running too warm you can lower the zip on the outer to let some heat out while retaining the protection of the inner.

The double layer only covers the front, with the rest of the jersey more conventional in design. The back is made of a material called Nanowarm, fleeced on the inside with a nanotechnology rain protection panel on the outside. This panel is highly breathable, as your back doesn't generally need as much wind protection. A single layer of Windstopper 150 fabric is used for the arms.

Just like the Gabba, when it's cold the Alpha Wind is much more comfortable with a baselayer. Castelli says it's suitable for use between 8 and 15°C, which more or less matches my experience. Towards the upper end I was okay without a baselayer, but anywhere from about 11°C downwards I definitely needed one. I have other winter jerseys I can wear in colder conditions without needing a baselayer, so I think Castelli has missed the mark with its claims of this being a thermal top you can wear in colder conditions than other winter jerseys.

The shoulders and sleeves are where I found a baselayer was most needed. Lacking a fleecy inner surface, the Windstopper 150 doesn't feel especially cosy against the skin, especially if you're chilly. Stick a decent baselayer underneath and it's very comfortable, offering an effective barrier to the wind.

There's reasonable water-resistance too, thanks to a durable water-resistant (DWR) coating. I wore it for an hour in steady rain, after which my core was pretty dry thanks to the extra layer on the front, although the rain had made its way through the single-layer sleeves and wetted the baselayer I was wearing underneath.

Let's compare the Alpha to the long-sleeve Gabba, then, as they're priced similarly. I found the double-layer front section on the Alpha warmer than that on a Gabba, whereas the sleeves here offer less protection. I have both in a large size, and the cut is quite different. The Gabba was conceived by racers and has a real racer's cut with zero flapping around at speed. It's not restrictively tight but it sits closely and aerodynamically against the skin. The Alpha is fitted, but noticeably less close to the skin and more accommodating of a variety of body shapes. It feels less speed-focused than a Gabba.

While the Gabba would be my preferred choice for racing, I really like some of the details here. The collar is just lovely; made in two sections of soft and cosy fabric, it does a great job of keeping the chilly air outside without ever feeling constrictive. It's about the most comfortable I've found on a winter jersey. The sleeves are a good length, too, with very comfortable stretchy cuffs – no draughts here.

>> Check out our guide to winter cycling jerseys here

Around the back there are the regulation three pockets, plus a cute little key pocket with a stretchy flap across the top instead of a zip. Below the pockets, the dropped rear section of the jersey is really stretchy with a large silicone Castelli logo print on the inside. It clings to your hips, doing a cracking job of keeping the bottom of the jersey in place, even with the pockets loaded. Oddly, there are no reflectives at all. Generally Castelli does a decent job with well-placed reflectives so this is a surprising omission.

There's a further pocket at the front, with a water-resistant zip. It's big enough for a phone or for a couple of gels, and is a bit easier to reach than the ones around the back.

This, then, is a really well-made jersey for riding in the cooler months. The double-front design is a novel idea. Sure, you could achieve a similar flexibility with a gilet, but here it's all in one garment. It's not really a racer's top, as it's more generously cut and with less of a focus on aerodynamics. It's also not really a super-warm thermal jersey, which is how I'd have interpreted Castelli's claims for it. Don't write it off, though. Suitably layered-up for the prevailing conditions, it's a real pleasure to wear. It is Castelli's most expensive jersey, and if you're spending that sort of money, you'll be expecting a lot. It doesn't disappoint – the detailing is as good as any jersey I've used and the Windstopper fabric offers great protection for something fairly lightweight.

Verdict

Not the super-warm top Castelli says it is, but a great outer layer when you don't quite need a jacket