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Castelli Idro Jacket



Ultra-packable rain jacket which makes great use of Gore's new fabric and offers very good breathability

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

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Manufacturers aren't always shy of hyperbole when launching product and the innovative Gore-Tex Active fabric used in this new Castelli Idro waterproof jacket has been described elsewhere on this site as a Game Changer. So it's refreshing to see Castelli taking a different approach and eschewing such... oh no, wait, my mistake, here's what it says: "Finally, the miracle jacket is here."

This is the third of the select group of cycling jackets made with Gore-Tex Active that we've tested, after being impressed with the Gore One and the 7Mesh Oro. The fabric is common to all three jackets, with just the details, fit and (to some extent) pricing to separate them.

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Here's what we said back when Castelli launched the Idro last year, in case you missed it. The standout feature is the use of a new 2-layer version of Gore's lightweight Active fabric rather than the more common 3-layer. Where previously you generally had an outer textile layer with some type of DWR treatment, here the membrane is outermost with a waxy "permanent beading surface", to shed water. Gore's coined the SHAKE-DRY™ designation to convey the fact that the outer surface simply doesn't absorb any water.

Castelli Idro Jacket - riding.jpg

Can you shake it such that it's literally dry afterwards? Well no, you can't. I tried, at some length. Post-shake, the outer surface remains damp, but without a fabric layer for the moisture to soak into, it dries really fast if you continue wearing it after the rain stops.

Castelli Idro Jacket - sleeve logo.jpg

The upshot of the new fabric tech is that it's lighter and folds down way smaller than other waterproof jackets. To give you an idea, this folds significantly smaller than any of the gilets I own, such that it will fit in a jersey pocket and still leave room for some other stuff. I've tested other jackets which pack down this small, but this is the first proper waterproof, and it's a hell of a feat.

Castelli Idro Jacket - back detail.jpg

What that means is you can comfortably cram it in a jersey pocket even on those rides where there's only a 20 per cent chance of rain, and then when that rain inevitably arrives, you can stay dry. I've worn the Idro in some deluges and the water doesn't get through at all. Although, let's be honest, the same can be said of significantly cheaper seam-sealed hardshells; a waterproof barrier is not the standout feature here.

Castelli says that the 2-layer Active fabric is the most breathable Gore-Tex ever made, and that is the holy grail of waterproofs – a jacket that keeps the rain out while allowing your sweat to get out too. I've been testing this in the late spring and summer months, when it's tended to be warm. I've worn it on days from around 14°C to the mid-20s. At the cooler end of that scale, the inside stayed dry even on hills, which makes things really comfortable – impressive. Once you're in the 20s, well, that's a tough gig for a hardshell – if you're pushing on, you generate generous warmth and humidity, and that's got to go somewhere.

Castelli Idro Jacket - hem.jpg

From about 18°C and upwards, I found sweat would build up inside and I'd end up fairly wet unless I was pottering. I think that in terms of outright breathability, the bulkier Velocis Stormshell from Bontrager performs better. But in reality, on hot, wet days, a hardshell is arguably not the right choice, and a lightweight DWR jersey is probably a better option. Hot, wet days being not all that common in the UK, there were lots of other days where the Idro hit the spot, and there were more of those days where I had it with me because it packs so small.

The lightweight fabric gives it a floaty feel when you put it on dry, and it is a quiet and unobtrusive jacket. The fabric isn't elastic, and so some fairly complex pattern-cutting has been used to ensure a good fit. The cuffs are partially elastic and they stayed in place well, and in fact the sleeves were of a good length such that I never found them flapping around my forearms. Putting the Idro on and taking it off is relatively simple – I could manage it while riding – once I'd got over the initial fear that the thin fabric was going to tear as I yanked it over my hands.

Castelli Idro Jacket - back.jpg

An obvious question if you were thinking of buying this would be how long it would last. I've had it for about three months and it's been worn 20 times or so. Quite a lot of the testing period was stubbornly devoid of rain, and so I commuted with it in the bottom of my pannier every day, kicking around with my lunch, a pump and some other bits and bobs. It's been through the wash half a dozen times and after all this, it seems pretty much in the same condition as when new. Castelli does say that this is specifically a road cycling jacket, and that implies that it doesn't think it would cope with mountain biking.

Castelli Idro Jacket - chest.jpg

A couple of nice touches that were unexpected and welcome on a minimalist jacket. First, there's an angled waterproof zip behind the right hip, which allows access to the right-hand jersey pocket while riding. It's not as easy as reaching round without a jacket on, but it makes grabbing a hasty gel without stopping possible. Also, I liked the well-positioned and sizeable reflective panels on the rear, especially given that the fabric used here is currently only available in black.

Castelli Idro Jacket - pocket.jpg

In terms of competition, the obvious contenders are mentioned above, with the same innovative fabric. All are expensive, all are only available in black, and all perform similarly well. Yes, the price is pretty high, but it's not a whole lot more than the Pave jacket I tested last year. That also combined total waterproofing with good breathability but wouldn't pack down as small and consequently doesn't get used as much. If the price is too steep then it's worth looking at the Sportful Hot Pack NoRain jacket, which is usefully cheaper and packs down to a similar size. I'm also a big fan of Bontrager's Velocis Stormshell I mentioned earlier. It's nowhere near as packable, but in terms of breathability while being waterproof, I think it's perhaps still the one to beat. Likewise, it doesn't pack down that small, but Endura's FS260-Pro Shell is another to consider.

> Survival tips for cycling in the rain

In conclusion, the Castelli Idro makes very effective use of the new Gore fabric and is comfortable and very nicely fitted. It staunchly keeps the rain outside and does an impressive job of moving moisture out. The biggest selling point for me is how small it packs, meaning that there's no reason not to have it with you. Miraculous, though? Not for me, Clive.


Ultra-packable rain jacket which makes great use of Gore's new fabric and offers very good breathability

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Make and model: Castelli Idro Jacket

Size tested: Large

Tell us what the jacket 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 says:


Finally, the miracle jacket is here. At only 120 grams it offers full Gore-Tex® waterproof protection, the most breathable Gore-Tex® ever made and permanent water repellency - and it all folds down to fill just half a pocket. Now you don't have to choose between a small jacket or a protective one to carry with you. We gave it a close-to-body race fit and functional details like the YKK® waterproof Vislon® zipper and a zipped opening to access your jersey pockets.

Tell us some more about the technical aspects of the jacket?

Castelli lists these features:

The lightest Castelli GORE-TEX® Product ever made

Durably waterproof and long-lasting weather protection backed by the GUARANTEED TO KEEP YOU DRY™ promise

GORE-TEX® SHAKEDRY™ product technology

Folds into just half a pocket

YKK® waterproof Vislon® zipper

Zipped opening for access to pockets

Anatomic wrist closure

Reflective seam taping

Weight: 123g

Rate the jacket for quality of construction:

Very well done. You can see that thought has gone into the panel shapes to give a fit which is close but not restrictive. The fabric is unusual, with a waxy surface on the top. The zipped access to the right hand rear pocket is unusual and a nice touch on a super-lightweight jacket.

Rate the jacket for performance:

Protection from the wind and the rain is excellent, as is packability. It's reasonably aero for a waterproof, although the lack of stretch means it's not nearly as close fitted as something stretchy could be. Breathability with a dry outer surface is impressive, although if you're working hard on a wet day you will still get damp inside.

Rate the jacket for durability:

It's survived kicking around in the bottom of my commuting pannier for three months which is a decent sign, but if I'm honest, I'm not convinced it'll be unscathed after three years of regular use, as it's just so lightweight.

Rate the jacket for waterproofing, based on the manufacturer's rating:

Castelli says that it's very waterproof and I'd agree.

Rate the jacket for breathability, based on the manufacturer's rating:

Better than most, and exceptional when it's dry, but not the miracle that it claims. When the outer surface is wet, humidity builds up more – once the rain stops, the outer surface dries quickly and that helps restore breathability.

Rate the jacket for fit:
Rate the jacket for sizing:

As I'd expect for Castelli. So a large is a close fit on me. I found the cuffs a bit too tight such that it made it difficult to put on and remove, especially when wearing gloves.

Rate the jacket for weight:

Very, very light for a jacket with full waterproof protection. The Gore One jacket is lighter still, but not by a lot.

Rate the jacket for comfort:

The inner surface feels pleasant against the skin as long as you're not working up a proper sweat, and the sheer lightness of the fabric makes it feel almost not there.

Rate the jacket for value:

It's a bit more than the Gore jacket and a similar price to the 7Mesh jacket which are both made from the same fabric. I'd argue that the step change in packability thanks to the Active fabric means that this measures up reasonably well against similarly priced high-end waterproofs from previous years.

How easy is the jacket to care for? How did it respond to being washed?

Seems to cope well enough. I've deliberately been careless to try to accelerate the process and it still looks new.

Tell us how the jacket performed overall when used for its designed purpose

Does a super job of keeping rain off, and the stashability means you've no excuse not to have it with you if the weather is uncertain.

Tell us what you particularly liked about the jacket

Packability, great rain protection, decent breathability and good fit. Oh, and the well-positioned reflectives too.

Tell us what you particularly disliked about the jacket

Nothing major. Tight cuffs, has a rather creased appearance.

Did you enjoy using the jacket? Yes

Would you consider buying the jacket? Yes, although probably only in the sales.

Would you recommend the jacket to a friend? Yes

Use this box to explain your score

This is priced at a point which I'd really struggle to justify, but if I could afford it, I'd be tempted. Performance is about as good as it gets for a hardshell right now, and that makes it exceptional, I'd say.

Overall rating: 9/10

About the tester

Age: 37  Height: 188cm  Weight: 78kg

I usually ride: On-one Bish Bash Bosh  My best bike is: Rose X-Lite CRS

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: road racing, time trialling, cyclo-cross, commuting, touring, club rides, sportives, general fitness riding, fixed/singlespeed, mountain biking

Jez spends his days making robots that drive cars but is happiest when on two wheels.  His roots are in mountain biking but he spends more time nowadays on the road, occasionally racing but more often just riding. 

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fenix | 5 years ago

£156 currently at sigma sport if anyone's tempted.

grantpet | 6 years ago

I bought one of these jackets to eplace a sportful hotpack and after wearing twice a small sliver of material had peeled away on the back lift shoulder- which began to tear away. Tredz were great and replaced the jacket after I had sent in a photograph. The jacket is completeley waterproof. In downpoors however such as I had on days 2 and 6 of a recent LEJOG you will still get your jersey wet as water ingresses from your shorts all up to your jersey. nothing gets through though and you can waer it all day without boiling in the. the fit is great for a rain jacket- snug and the cuffs are elasticated- I'm still very cautious when putting it on and taking it off over my big mitsbroken heart

Dr_Lex | 6 years ago

Evans price of just over £200 makes it more bearable, but I'm holding out for a coloured version of the fabric for a greater WAF.

jaysa | 6 years ago

Looks nice, but mad money! Does Castelli think we are all wealthy - this costs £2 per gram fgs.

I'll be sticking with my Sportful HotPack No Rain as suggested, bought on sale ...

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