Castelli Alpha 150 Jacket Review 2026: Winter Layer for Triathletes
The Castelli Alpha 150 is a two-layer winter jacket for cold, dry-to-damp training rides. Castelli pairs a Polartec AirCore outer with a Polartec Alpha insulating liner, and rates it for -2°C to 10°C. That covers most of a British autumn and winter for triathletes who keep riding outdoors. We have not tested the jacket ourselves, so this page draws on Castelli’s spec sheet, the Tredz listing and published reviews.
Price check: Tredz lists the Alpha 150 at £200 against a £360 RRP at time of writing (28 September 2026). Prices and stock change, so check the current figure.
Key features
- Two-layer construction. The outer is 150g Polartec AirCore, which Castelli describes as windproof and rain resistant while staying breathable. The liner is Polartec Alpha insulation, which holds warmth and moves moisture out.
- Temperature range. Castelli rates it for -2°C to 10°C.
- Zips at both ends. Top and bottom YKK zips let you vent from the waist or the collar. Castelli lists a wind and rain cover over the zip.
- Pockets. Three rear pockets with reflective piping, plus a zipped valuables pocket.
- Fit and weight. Tailored, close to the body. Castelli lists 318g for the men’s jacket.
- Materials. Recycled yarns and a PFAS-free finish, per Castelli and Tredz.
How it handles rain
Castelli calls the jacket rainproof and suitable for most conditions except all-day heavy rain. Cycling Weekly’s review takes a more cautious line: its headline praises the cold-weather protection and says the water repellency could be considered overrated. Read it on Cycling Weekly before you rely on this as your only wet-weather jacket.
Who it suits
- Riders who train through winter on dry-ish days. The temperature rating and breathability suit long, steady rides more than stop-start commuting.
- Riders who already own a shell. If you have a separate waterproof (see our waterproof jacket guide), the Alpha 150 can be the warm layer for the days when rain is unlikely.
- Riders who want one jacket for a wide range. The zips let you open it up as the temperature climbs toward 10°C.
Sizes and availability
Tredz lists sizes XS to XXXL and three colourways when we checked: Brilliant Orange/Dark Grey, Deep Bordeaux/Clay and Light Black/Black. A women’s Alpha 150 is also listed at Tredz.
For the rest of your winter kit, see the best bib tights for winter training, winter cycling gloves and our Castelli Perfetto RoS 3 review.
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