What it takes to make the yellow jersey – Inside Castelli’s new partnership with the Tour de France

For a clothing manufacturer, the Tour de France is a big deal when it comes to getting eyes on its brand and products, but it also means it has to deliver enough of their best kit to riders performing in the biggest race in the world.

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When a rider moves into the lead of any classification, they’re given a variety of kit to see them through any preference or eventuality. First there’s a race jersey, which they’ll be expected to wear with their own team shorts, though there’ll be two weights available to cater for the weather.

Most riders race in one-piece race suits these days, and there are two weights of those available as well, with a new one issued every couple of days if the rider still qualifies to wear it. And on top of that there’s a gilet, short-sleeved Gabba jacket and a long-sleeved rain jacket.

But perhaps the most talked about piece of kit issued to classification leaders is the time trial skin suit. With the perfect fit and a suit’s aerodynamics the subject of much discussion, we’ve even seen conjecture that GC riders might avoid leading a race in order to avoid ill-fitting kit. So how does Castelli hope to ensure its suit is one that helps rather than hinders riders?

“At the top levels now, each rider has spent countless hours perfecting their suit, but if teams are being honest, there’s a lot of times you can put somebody into a suit you don’t know and it throws up some great numbers,” Smith continues. “And our suit at the Tour de France has been consistently very fast across a very wide range of people. So nobody’s going to be racing in a poorly designed suit.”

Elisa Balsamo rides the time trial during the 2026 Giro d’Italia Women wearing a Castelli skin suit. (Image credit: Getty Images)

Castelli was around long before its first foray into supplying Grand Tour leaders’ jerseys, indeed, the company traces its history way back to 1876, when Vittore Gianni began his tailoring business in Milan, dressing football teams like AC Milan and Juventus, and even the Milan Ballet.

As part of the deal with ASO, Castelli recently launched its ‘Maillot Jaune’ line of kit. It’s not all yellow, and even the yellow they do use is different to that which we’ll see the Tour leaders wearing next summer, but it is a good example of the kind of effort that goes into producing a new consumer line.

“There was an incredible amount of work that went into that kit,” Smith explains. “Trying to make it stretchy enough, but not too much because you make it too stretchy, it starts to sag. We’ve always made jerseys with limited stretch on the back to keep your jerseys or your pockets from sagging.

“But we knew we wanted to fit the widest range of people with the maximum amount of comfort, we wanted to make that fabric more stretchy than we’ve ever done before, both in width and in length. So we’ve actually kind of re-engineered the way we engineer the pockets by tightening up the waistband, so we’re holding the pockets from below rather than above.”

You can have all the striking and innovative designs you like, but any cycling kit company must live and die by how comfortable and durable their shorts are. While Castelli’s prototyping group will put most new items through four or five internal samples, shorts take far longer.

“They have about double the total production time because so many things could go wrong by doing it wrong, we feel it a lot more, so it’s obviously quite a bit quicker on a jersey than on a short. But yeah, shorts will take a good year and a half in the production cycle,” says Smith, before revealing the as-yet un-released shorts he wore earlier that day went through 14 rounds of samples.

For now at least, the only bits of Castelli kit you’re unlikely to be able to buy are the jerseys the brand will make for the Tour de France and Tour de France Femmes for the next few years: “We don’t think there’s really that much of a market for it,” Smith says.

Editorial note: Cyclingnews attended the Castelli/ASO launch on an imedia package from Castelli that included travel and accommodation. In line with our editorial standards, our coverage is independent and was not subject to review, approval or influence by the organiser or any sponsor; no favourable coverage was promised or given in return.