Castelli Insider Jersey review
A super lightweight jersey for the steamiest of indoor sessions that can also be used outdoors on hot days
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The Castelli Insider Jersey is highly breathable and, although intended for indoor training, can also function as an ultra-lightweight jersey for hot summer rides. If it weren't for the silicone gripper in the hem, which is disproportionately tight, this would otherwise be perfectly fitting jersey that performs well in its intended scenario.
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Super breathable
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Two rear pockets
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Doubles as a summer jersey
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Disproportionately tight around the waist
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The Castelli Insider Jersey is the lightest jersey (opens in new tab) the Italian brand has ever made, and it certainly feels that way – there really is nothing to it. Designed for indoor training when modesty requires a top, it should also make a pretty handy hot-weather jersey come a summer heatwave.
Castelli Insider Jersey: construction
The fabric is a semi-open mesh which, while not entirely see-through, doesn’t leave that much to the imagination. That said, there is enough opacity that it does do its job of keeping you decent when you can’t go topless.
With two pockets on the rear, not only are phones and chargers easier to transport to your turbo setup but taking the jersey out on road rides is a genuine possibility. That said, the jersey is not SPF rated, so suncream will be a necessity for outings in the summer sun.
At the hem, the silicone gripper is wide and effective at locking the jersey in place, but it does feel noticeably tight. The cut of the jersey is supposed to be figure-hugging and this is achieved across the shoulders and chest without stepping over into feeling restrictive – in juxtaposition to the hem.
The sleeves are shorter than the current fashion of just above the elbow, coming halfway down the bicep, and the collar is a little lower than usual on a short-sleeve jersey.
The ride
Coming from not using a jersey at all for indoor rides, although this jersey is incredibly thin, there is still a discernible difference when the fan is first turned on. You do feel slightly more isolated from the wind.
>>> Best turbo trainers (opens in new tab)
But after a few minutes on the turbo, you soon get used to the jersey. The difference is comparable to a 1°C variation in room temperature: noticeable if a sudden change; imperceptible once you’ve gotten used to it. Even in frenetic Zwift races I didn’t overheat, and the jersey didn’t cause any distraction from the efforts.
Although the hem does feel disproportionality tight when putting on the jersey, it wasn’t actually noticeable once riding along. Although when you do unzip the jersey fully, it does open with a ping.
The pockets performed quite well, managing to hold a phone, Allen keys and even a laptop charger. There was a fair degree of sagging when stuffed to the brim, but nothing more than you would expect from such a lightweight jersey. Having somewhere to stash the surprising quantity of paraphernalia that indoor riding can require proved to be a genuinely useful function of this jersey on multiple occasions.
Given that I was testing the jersey in the later part of autumn, I didn’t assess its performance on any rides outdoors. But from my experience so far, I am fully confident that it would work excellently as an ultralightweight jersey for super-hot conditions.
Value
At £75, the Castelli Insider Jersey compares favourably to the Le Col X Wahoo Indoor Training Jersey (opens in new tab) which is £120 and has the downside of arm grippers that are prone to getting sweaty.
But if all you’re after is something to cover you up when on the turbo, the Endura Fishnet would provide this function for only £29.99. However, in being a base layer, it is less versatile than the Castelli Insider Jersey as it won’t double up as a jersey of the peak of summer.
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After winning the 2019 National Single-Speed Cross-Country Mountain Biking Championships and claiming the plushie unicorn (true story), Stefan swapped the flat-bars for drop-bars and has never looked back.
Since then, he’s earnt his 2ⁿᵈ cat racing licence in his first season racing as a third, completed the South Downs Double in under 20 hours and Everested in under 12.
But his favourite rides are multiday bikepacking trips, with all the huge amount of cycling tech and long days spent exploring new roads and trails - as well as histories and cultures. Most recently, he’s spent two weeks riding from Budapest into the mountains of Slovakia.
Height: 177cm
Weight: 67–69kg
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