The Castelli Alpha is a very good windproof jacket that offers plenty of temperature regulation thanks to a clever design feature.
What is this 'clever design feature' of which I speak? Castelli has separated the insulation layer and the windproof layer at the front of the jacket.
The outer layer is windproof. Open it up and you reveal an inner layer that isn't windproof, it's made from a fleecy polyester/elastane. If you're still too hot you can open up this inner layer too and really let the cool air in.
The outer layer is made from Windstopper 150 which, as you'd expect from a Windstopper fabric, blocks cold air out completely. It's also highly water resistant. The Alpha isn't waterproof but it will keep you dry on those drizzly days that the UK does so well, and road spray just beads up on the surface and rolls off. Proper rain will gradually get through, first at the untaped seams around the shoulders and the fleecy neck, so you'll need to carry an outer shell if the forecast is looking really wet.
The inner layer, which extends across the front and down the tops of the sleeves, adds a lot of warmth, and much of the collar is fleece-lined.
The bottom of the body section and the cuffs are another fabric again. It's a really stretchy, raw-edged polyamide/elastane that is low bulk and fits closely.
All of the other fabrics are stretchy too, including the Windstopper 150, so the slim fit doesn't feel tight whatever position you're riding in.
Castelli gives the Alpha a temperature range of 0°C up to 12°C, and I'd say that's about right. Personally, I'd have to add a mid-layer for those lower temperatures, although I run cold. Maybe you'd manage with the jacket over just a baselayer.
Castelli's idea of keeping the windproof layer and the insulation layer separate works well to keep you ventilated, and a yoke vent improves breathability around the back. It's particularly impressive if you encounter a range of temperatures over a long ride or, more likely, your body temperature varies as you tackle different types of terrain, so you can stay comfortable whether you're climbing, descending, or riding on the flat.
What's the advantage over simply wearing a windproof jacket over a jersey? Well, the fact that the two layers are connected, along with the close fit, means there's very little flapping or billowing when you open the outer zip.
The Alpha comes with three big pockets at the rear, elasticated binding around the tops helping to keep your stuff safely inside. There's a zipped pocket back there too for your phone, cash or keys.
You also get a little zipped pocket at the front, although I never got into the habit of using it. I just prefer to keep everything around the back where it's out of the way.
The YKK front zip on the outer layer comes with a storm flap over the front and an easy-to-grab puller, although the zip puller on the inner is a bit more fiddly if you're wearing thick gloves. Still, you're far less likely to want to adjust that one.
Exceptionally good jacket that'll keep you comfortable across a range of temperatures
road.cc test report
Make and model: Castelli Alpha 'Winter' Jacket
Size tested: Large, BlueStone/Black
Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Castelli gives the Alpha jacket a HUGE write up:
"Throw out everything you think you know about cycling jackets and redesign the way a jacket should be made. Or possibly how they'll all be made in a few years when everyone else follows our lead once again. The name Alpha denotes the first in a series. In these products we're introducing several new techniques and fabrics to construct cool and cold weather jackets. We've focused on two perennial problems with cycling jackets and wind jerseys. First is ventilation.
"With our latest fabrics we can essentially build a winter jacket that will keep you warm in all but the most extreme conditions with just a base layer underneath. But when you open the front zipper you get a blast of cold air at the top of your chest, while the rest of your body remains too hot.
"In Alpha we've detached the insulation layer from the windproof layer so that you can open the windproof layer to let air in to ventilate and help evaporate moisture. Riding these pieces shows how effective it is at regulating temperature and comfort while helping to keep you drier.
"The second focus area is all the openings. At the waist we have a new fabric and construction that lays completely flat, is streamlined for aerodynamics, yet when you drop into the riding position it follows your body without binding or billowing. At the wrists we have a new flat raw-edge construction that interfaces perfectly with our gloves to keep drafts out and to improve comfort. At the collar we have a new articulated construction that follows the bends in your neck whether you're standing or riding in the lowest aero position."
Tell us some more about the technical aspects of the product?
Castelli lists these features:
- Articulated collar that fits better whether standing or riding
- Windstopper 150 fabric is windproof and water-resistant, with four-way stretch for freedom of movement
- Better ventilation, better moisture evaporation thanks to separate insulating layer
- Asymmetric external YKK Vislon zipper slides easily and lays flat
- Raw edge waist lays flat and moves with you
- Raw edge wrist cuffs lay flat for a perfect interface with gloves
- Stretch fabrics with advanced patterning make for excellent close-to-body fit yet accommodates a wide range of body types
- Back ventilation
- Castelli silicon text gripper at waist keeps the jacket from riding up
- 3 rear pockets, one zippered with reflective webbing
It's a very good system that's executed well.
A Windstopper jacket built to quite a complicated design is never going to be dirt cheap.
Tell us how the product performed overall when used for its designed purpose
It's an exceptional performer for cool and cold days.
Tell us what you particularly liked about the product
The fit, the double front layer, the water resistance... There are lots of good points.
Tell us what you particularly disliked about the product
Past experience suggests that the logo around the back will star to crack fairly soon.
Did you enjoy using the product? Yes, it's excellent.
Would you consider buying the product? I would.
Would you recommend the product to a friend? Yes
Use this box to explain your score
This jacket puts in an exceptional performance to keep you comfortable across a range of temperatures. It's worth the price.
About the tester
Age: 43 Height: 190cm Weight: 75kg
I usually ride: My best bike is:
I've been riding for: Over 20 years I ride: Most days I would class myself as: Expert
I regularly do the following types of riding: commuting, club rides, sportives, general fitness riding
Mat has worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.