Rab’s new Cinder Kinetic Waterproof trousers are made from, hands down, the best waterproof material I’ve ever tried. That is one hell of a bold statement given I’ve been striving to keep the Yorkshire rain out for at least a decade, but Rab’s Proflex fabric is astonishing. That helps make it one of the best mountain bike trousers we’ve tested all winter.

Before we get to why, you need to know a little bit about the brand to understand why the Kinetic trousers don’t get full marks, dispute this wundermaterial.

The elastic waist tensioner isn’t very stiff, but I had no problems with it even after months of use

Launched last year, the Cinder range is mtb specific, but of course Rab itself has decades of heritage making outdoor gear. In fact, the mtb project was driven by the UK firm’s staff, who’d been cherry picking the best bits for mountain biking for years. 

Using selected key pieces and fabrics from the regular line up as a foundation, the brand formed a team and set about refining and perfecting pieces specifically for cycling and the Cinder range was born. 

With a 3-layer Proflex fabric, this Kinetic Waterproof trouser comes in two colours and two leg lengths (a trend started by Alpkit and its excellent and wallet-friendly Floe Trouser) and is a key Cinder piece.

Details and specifications

Rab’s cut is reasonably close-fitting and the softish fabric is quiet, super stretchy and unrestrictive while pedalling with enough give to fit slimmer knee pads. The waist band has a higher back for comfort and to keep spray out and double poppers at the fly for extra security. 

The ‘shock cord’ waist tensioning design is effective, although the elastic on the small tensioner isn’t particularly stiff. At first I was worried it wouldn’t hold out over multiple goes in the machine, but I’ve been riding in these for months now without any issue.

There’s no tapering below the knee of these trousers, which makes them look a bit more like walking trousers

The Cinder Kinetic lower leg has a long zip for easy removal when muddy. Together with the loose fit below the knee and the two tone colour option, that lends the Kinetic an outdoor look. 

In fact, the styling and construction feels a bit more targeted to XC or gravel riders than enduro or e-bikers, who are constantly in mud and at risk of crashing. It’s led to a new nickname for me, I’m now called ‘scout master’ out on the trails. I’m not a huge fan of the baggy cut then, and the blue colour isn’t as easy to keep clean as the black I’d prefer either.

In terms of the main trouser fabric, it’s fully waterproof with a huge 35,000 breathability rating, although some reinforced panels use a thicker, tougher and more waterproof (20k) material on seat, inner thighs and driveside hem that’s slightly less breathable. 

Rab developed its Proflex fabric inhouse with a incredibly thin, very stretchy, PU layer. It’s solid (unlike typical microporous membranes like Gore-Tex) and works by attracting moisture to its inner surface and moving it outside in a process of osmosis, rather than allowing vapour to pass through like most designs. This allows Rab to ‘make softshells with the waterproof protection of a traditional hardshell’ and the brand claims that as you sweat more, the membrane responds more to equal the balance of water on each side of its fabric.

Rab’s Proflex fabric is breathable yet incredibly hard-wearing

Performance

Out riding, the supple Proflex material means freedom of movement is as good as anything on the market for a 3L waterproof. Breathability is so effective any heat and sweat build up gets pumped out as fast as it’s generated. Temperature management is so good in fact, I’d happily wear these most of the year, since they aren’t really that much warmer than regular riding trousers.

In heavy rain and deep puddles, Rab’s thin and stretchy softshell is really protective and only gets damp in a few spots after some serious hammering. 

The more I’ve used the trousers, the more impressed I’ve been. It would be hard not to, after an uplift day at BikePark Wales in torrential rain, that left me with a dry bottom half. That is a neat trick, and very rare for any waterproof, when you’ve been sitting down and pressing moisture into the fabric in the uplift bus.

I felt the portion of the trousers below the knee was too baggy and not tapered to the ankle enough

Get the Kinetics wet (it’s hard not to at the moment) and the material gets darker and look like it’s about to wet out in spots. And yet the pant never leaked to the extent the vast majority of rivals do; instead, moisture somehow stays trapped in the fabric. 

Rab’s trick seems to be linked to how breathable Proflex is and its ability to expel so much moisture from inside, the trouser never gets too heavy or clammy. The fabric is basically so quick drying, it literally changes shade as you’re rolling along.

In terms of breathability and water and wind protection, this Cinder Kinetic offers unreal performance. My only main bugbear is the portion below the knee is too baggy and not tapered in enough to the ankle. It doesn’t exactly get caught in the chain, but it gets heavy and pulled out of shape when repeatedly doused with mud and rain. 

Despite the reasonably thin and lightweight fabric, Rab’s trouser has survived plenty of vegetation rubs and snagging, but I have put a tiny rip in the fabric on the inner calf somehow. For an investment of over £200, a slightly more robust and warmer pant might offer extra protection for gravity MTB or e-bike riders in deep winter, but my guess is that would impact on what’s so great about the performance here.