Castelli Idro 3 – Levelling Up The Ultimate Cycling Waterproof

14 October 2021

By Nicki Giles

Man riding bike in Sportful Super Jacket

The Castelli Idro 3 cycling jacket is the brand’s best performing packable and breathable waterproof ever. Here’s why it should be in every rider’s pocket.

The newly launched Castelli Idro 3 Jacket is billed as a ‘game changer’, since it adds further valuable features to an already incredible weatherproof jacket that Cycling Weekly gave the full 5 out of 5 stars and described as offering “Superlative performance in a tiny package.” We’ll give you a run-down of all the new features and exactly what makes this peloton-leading jacket so exceptional.

Man riding bike in Sportful Super Jacket

The Castelli Idro Jacket – already a legend

When it burst onto the cycling scene, the Idro Jacket caused something of a sensation. The material used in its construction, Gore-Tex Shakedry, is truly something special. Traditionally, full waterproof jackets are composed of three layers, with the waterproof layer sandwiched between two bolts of material. Gore-Tex Shakedry is different, as it is made up of a layer of PTFE with a single layer of woven microfiber nylon 6.6 below it.

As a result, it is not only well and truly waterproof, having successfully passed the ISO 6630 waterproofing durability test of 500 hours of continuous rain, but highly breathable, as the fabric’s not heavy enough to keep sweat trapped inside. It’s also incredibly thin, weighing just 49g per m².

This made the Idro jacket the ultimate ‘just in case’ bit of cycling kit, as it offered the bomb-proof protection needed when pedalling through a cloud burst or freewheeling down a misty mountain slope, without being too big to risk not using. In fact, the finished jacket folded into the space of half a pocket!

Since the fabric isn’t stretchy, Castelli had to pull off some wizardry to ensure a close fit while maximising freedom of movement, for example by including elastic cuffs at the sleeves. The designers also worked hard to ensure the jacket remained minimalist and compact, but never at the cost of functionality. For example, a rear pocket with a waterproof zip was considered ‘acceptable weight’, since it would allow the wearer to carry the sundries needed for a day ride.

Man riding bike in Sportful Super Jacket

Evolution of the Castelli Idro 3 Jacket

While the Idro 2 was designed to be a particularly lean, no-frills racer version of the Idro, the Castelli Idro 3 Jacket has a few added features to make it truly indispensable for any cycling enthusiast looking to ride all winter – all with negligible weight gain.

For a start, there’s the new, wider sleeve, making it easier to pull the jacket on and off. You also get an inner gaiter that grips your wrist, while the slightly longer sleeve drops down partially over your hand. In terms of functionality, this means you can pull a glove over the gaiter, then let the outer layer fall around the glove, forming a waterproof seal. No more stiff, frozen hands when your waterproof leaks at the wrist or you descend through cloud!

The next useful feature is a new panel at the back of the jacket, made of low-force, high-stretch Gore-Tex. This is designed to ensure a tight fit for lean climbers and Sunday riders alike, while also providing a bit of extra ventilation and some leeway to stuff your back pocket full of ride nutrition and essentials.

Another very worthwhile addition is reflective silver strips down the full length of the arms and reflective trim on the lower back. Since the fabric is black – one of the drawbacks of the fully waterproof PTFE layer is that it’s near impossible to get dye to soak into the material – these strips will go a long way towards maximising your visibility on those crack-of-dawn rides.

Castelli has added a YKK Vision AquaGuard zipper that keeps out water while being easy to open and shut, a high neck to lend additional warmth during those freezing descents, and welded neck and waist gaiters. The Idro 3 also offers extra length in case of rain and a cut that takes cycling position into account, cementing its status as a jacket designed thoughtfully by cyclists, for cyclists. 

Ultra-protection from the Idro 3

The Castelli Idro 3 Jacket brings serious improvements to a jacket that was already a game changer. After all, Cycling Weekly put the Idro 2 through its paces as part of a group test and concluded that it was “Without a doubt one of the best performing full waterproof rain jackets we have ever tested, let alone in the packable category.”

The only issue they could find with the Idro 2 was that there were no extra features to add versatility, although they declared in their 5-star review that “The performance more than makes up for any shortcomings.”

Now, the Idro 3 has such features. The reflective strips that make it safer for night use; glove compatibility and additional gaiters to allow you to tackle even harsher conditions without rain getting in or wind chill; and a cut that embraces different shapes and isn’t pared down to the basics, purely with serious racers in mind.

It’s a jacket that can handle any condition, from snow to sunshine, and that puts functionality above the label of ‘most lightweight’, while still weighing in at an impressively tiny 136g for the men’s medium size and 120g for the women’s small. Plus, the women’s version isn’t an afterthought – it boasts every scrap of functionality that the men’s does in a thoughtful, female-specific cut.

Man riding bike in Sportful Super Jacket

A road cycling staple

Since the Castelli Idro 3 jacket is phenomenally versatile and small enough to pack on every ride, here at Saddleback we pretty much keep ours permanently in a jersey pocket. That way, if the weather changes – which, let’s face it, happens a lot in the UK – we know we’ll be able to carry on cycling regardless! 

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