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Castelli's Diagonal Women's Jersey FZ is brilliant for dry, cool-to-cold rides. It does a great job of keeping you warm without excess bulk, and works well with layers to increase its weather-window of performance. Riders committed to performance-focused training will appreciate the levels of breathability this thing offers.
With some practical layering, a thermal jersey like this can be used for virtually every single training ride from autumn through to spring. The FZ is a snug fit, if not quite the race-fit of something like Sportful's Thermal Jersey, and the fabric is really not bulky either.
Consequently, while it performs perfectly well on its own, it can easily take a base layer (or two) beneath or a jacket, gilet or a waterproof on top.
I followed Castelli's sizing chart to test a medium (that's not me modelling it). It's a good fit all over, with a decent sleeve and body length and no tightness around the chest or shoulders. If you're between sizes, I'd say sizing up or down is probably pure preference - whether your want a bit of breathing room, or a very snug fit.
The collar is a good height and sits close to the neck; I can't get a neck warmer on and zip it up without feeling choked. It's not fleece lined here, but the fabric is soft enough (it's the same as the rest of the jersey), if a little less cosy. There's no zip guard either, though the doubled-over material running the length of the zip ensures your neck is not irritated.
The cut at the rear is generous, with an added strip of fabric to protect the lower back.
In a riding position, this jersey feels really comfy – there's no pulling or tightness anywhere. It moves well with the body, in and out of the saddle. The silicone strip at the rear hem helps prevent the jersey shifting under the weight of loaded pockets.
On its own, the FZ performs well in temperatures between 12 and 15 degrees. The polyester has a brushed, fleecy inner layer, so it's soft enough against bare skin too. Castelli suggests it can be used up to 18 degrees; obviously, I haven't managed to test this in the last four weeks, though I really wouldn't want to be exerting myself in it above 15 degrees. I started adding layers below 12 degrees.
With two decent layers, this is actually a decent bit of kit in temperatures as low as three degrees, as it offers exceptional breathability. Head out for some intense riding in colder temperatures and it really does shine. I found absolutely no moisture build up inside the jersey in such scenarios. Naturally, this is also a little dependent on the choice of base layer.
The FZ doesn't handle rain, but stick on a good waterproof and it continues to perform in terms of breathability. On the occasions I did get caught out (without a waterproof), there wasn't an immediate chill. You certainly wouldn't want to be caught in a prolonged cold shower though; there's very little in the way of windproofing.
I'd say Castelli has got the storage volume and positioning right on this jersey; the three rear pockets are generous and easily accessible. It's worth noting there's no zipped pocket, though.
There's only a small amount of reflective piping at the rear, too - not really enough to have an impact. The colour I tested scores highly on the visibility stakes however, although in foul weather I found myself having to use stain remover to get it sparkling again.
Still, I'd rather this than ride in dark kit that can render you invisible on a grim day. If you do want to be a little more subtle than this (or the light blue Celeste), Military Green or Light Black may appeal.
Of the three thermal jerseys I've tested so far this autumn/winter, Castelli's offers – by a good margin – the best fit and performance. No surprises it's the most expensive, though. It's a tenner more than Sportful's Bodyfit Pro Women's Thermal Jersey and a whopping £50 more than Altura's Women's Nightvision. I keep harping back to Liv's Race Day Thermal Jersey which impressed me with its performance, even if the cut was a little niche; the latest version is now £74.99.
I've been impressed with the breathability and versatility of the Diagonal Thermal Jersey FZ, and its great fit is the icing on the cake. It's a significant investment but, with supporting kit, it will serve you extremely well for at least three of our four seasons.
Close fitting fleecy jersey with outstanding breathability – it's expensive but worth it
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road.cc test report
Make and model: Castelli Diagonal Women's Jersey FZ
Size tested: Medium
Tell us what the product is for
Castelli says: "Our pro-level printed thermal jersey combines warmth with excellent moisture management. The graphic is designed to look good on its own or under a Perfetto or Aria vest."
Tell us some more about the technical aspects of the product?
-Maximum warmth from printable version of our Warmer polyester fabric with brushed fleece inner layer
-YKK® Vislon® zipper with protective tab at top
-3 external rear pockets
- 12°-18 °C / 54°-64°F
How easy is the product to care for? How did it respond to being washed?
Simple – in with the rest of the cycle gear.
Tell us how the product performed overall when used for its designed purpose
Really well with outstanding breathability.
Tell us what you particularly liked about the product
Tell us what you particularly disliked about the product
How does the price compare to that of similar products in the market, including ones recently tested on road.cc?
This is at the upper end of the price range. Liv's Flava and Race Day Jerseys are both cheaper, as is Altura's Nightvision. Only the like of Rapha and Assos pitch their thermal jerseys at a higher price.
Did you enjoy using the product? Yes
Would you consider buying the product? Yes
Would you recommend the product to a friend? Yes
Use this box to explain your overall score
Brilliantly breathable, well proportioned and versatile, the only thing that could be better is the price – it's a steep investment, but one that should pay off. It's very good.
About the tester
I usually ride: Road My best bike is: Carbon road.
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, touring, club rides, general fitness riding, Getting to grips with off roading too!
Emma’s first encounters with a road bike were in between swimming and running. Soon after competing for GB in the World Age Group Triathlon Championships in Edmonton in 2001 she saw the light and decided to focus on cycling.
After a couple of half decent UK road seasons racing for Leisure Lakes, she went out to Belgium to sample the racing there and spent two years with Lotto-Belisol Ladies team, racing alongside the likes of Sara Carrigan, Grace Verbeke, Rochelle Gilmore and Lizzie Deignan. Emma moved from Lotto-Belisol to Dutch team Redsun, then a new Belgian team of primarily developing riders, where there was less pressure, an opportunity to share her experience and help build a whole new team; a nice way to spend her final years of professional racing.
Since retiring Emma has returned to teaching. When not coercing kids to do maths, she is invariably out on two wheels. In addition to the daily commute, Emma still enjoys getting out on her road bike and having her legs ripped off on the local club rides and chain gangs. She has also developed an addiction to touring, with destinations including Iceland, Georgia and Albania, to mention just a few. There have also been rare sightings of Emma off-road on a mountain bike…