Castelli Alpha Flight RoS Jacket review

The Castelli Alpha Flight ROS jacket is pitched towards milder winter conditions and riders training with some level of intensity outdoors through the winter period.

A far lighter construction compared to the Alpha Doppio ROS jacket means you can maintain your body temperature across a wide range of conditions, and the breathability is excellent.

A practical arrangement of pockets means it works very well as a single outer layer – you only need to wear a cycling baselayer underneath.

There are potential issues with the fit, though, if you’re of a racier disposition.

Castelli Alpha Flight RoS details and specifications

The Alpha Flight ROS jacket is the lightest of Castelli’s Alpha double-layer jacket designs, sitting beneath the Doppio ROS and Ultimate ROS jackets.

It offers much less insulation and protection from the elements, but majors on breathability.

To this end, the outer Nano Flex fabric is single-layer thin, while the inner liner features thinner Polartec Alpha insulation.

Like the Doppio ROS I tested earlier this season, the inner liner is zippable. It extends around the back and most of the way down the arms.

The outer layer is said to be windproof, although the thinness of the fabric is intended to also promote air and moisture exchange to assist temperature regulation.

To this end, you won’t find a waterproof membrane here – just a DWR (durable water repellent) treatment to help splashes and light showers bead away.

The collar is mesh-lined for comfort without adding the warmth a fleece lining might.

On the rear, three full-sized pockets have reflective tabs, and there's a zipped mesh-lined security pocket on the rider’s left flank.

The outer full-length YKK zip features an easy-pull cord, although it’s not a double-zip model (so you can’t undo it from the bottom for added ventilation).

The fit is intended to be slim but accommodating – in line with Castelli’s recent tweaks to its garment cuts – and the low-profile, silicone-strip backed waist hem hints towards these aims.

The cuff is deep and elasticated, intended to fit under the cuff of winter cycling gloves easily.

The jacket weighs 291g in a size large, which certainly feels light given the number of layers, pockets and zips in the construction.

Castelli Alpha Flight RoS jacket performance

The Castelli Alpha Flight ROS jacket’s construction means it’s extremely breathable, which proved a boon in the mild conditions the jacket is designed for.

Castelli says the jacket has an ideal operating window of 6-16ºC (42-61ºF), and I’d largely agree with that claim.

At the higher end of that range, sweat wetted out the thin outer fabric from the inside, although it’s worth noting I was overdressed on my bottom half for those conditions.

At the lower end, I saw steam rising from my shoulders and upper back – indicating moisture and warmth have plenty of opportunity to escape.

This is the key point of the Alpha Flight ROS jacket, although the downside is precious little protection when the heavens open.

The DWR treatment is effective to begin with, but it struggles with heavier showers, and prolonged heavy bursts can see water seep through. After this, you’re left with a damp and cold-feeling cycling jacket.

In my view, the ROS (‘rain or shine’) title stretches credibility here, while the cut might not appeal to many of the riders the jacket is designed for.

Given Castelli says the Alpha Flight ROS is “extremely fast”, you might be hoping for a close, aerodynamic cut. However, that’s not really the case.

My torso is relatively broad for a cyclist, so I fill a large Alpha Flight ROS jacket reasonably well. However, those who are slimmer than me but require the length of a large-sized jacket will find the body quite baggy.

This sensation isn’t helped by the thin outer fabric, which has a tendency to flap in the wind. I found this particularly true on the arms, where the cut seemed too baggy.

Riding at pace in the wind, the flapping on the arms is audible and causes added resistance.

It might not bother everyone – I don’t care about aerodynamics when riding in the winter – but some riders will be left disappointed here.

So, for someone to part with £290 / $319.99 / €269.95 for a garment that seems to miss the mark in terms of fit, if not fabric performance, is a tall ask.

Castelli’s Alpha range of garments are notoriously expensive, but their winter performance has almost always justified their price tags.

However, while there's plenty to like with the Alpha Flight ROS, the execution may leave some potential buyers cold.

Perhaps the closest comparison for performance – given the double-layered approach is uncommon – is a long-sleeve winter jersey.

These are far cheaper, though, and a gilet could be employed when extra wind protection is needed.

Castelli Alpha Flight RoS jacket bottom line

High hopes accompanied the Castelli Alpha Flight ROS jacket when it landed at BikeRadar HQ – the reputation of previous and current-generation Alpha garments preceded it.

There are good points here. It’s practical, has a good operating-temperature window and breathes brilliantly.

That said, a slimmer, racier cut would be advantageous, while the relative lack of water resistance in an ROS jacket will make spending the required cash less appealing for many.