3RD ROCK Jeans - Fitz and Mercury Review

The 3RD ROCK Fitz and Mercury are extremely stretchy, high-quality denim climbing jeans. They both use the same EcoMORPH Denim but the cut and appearance of the jeans is vasty different. I was not keen on the look and feel of one; but the other have become my go-to climbing trousers. Between them they should cater to a range of tastes and leg shapes!

Fitz vs. Mercury

Before we launch in to the full review here's a quick summary - and visual illustration - of the difference between the Fitz and Mercury. The Fitz are blue denim and they have a 'carrot shape' design. This does what it says on the tin: they're wide at the crotch and roomy on the thighs, tapering down to become slim on the lower legs. The Mercury are black denim and have a much more regular 'slim jean' design - just like you'd expect from a pair of highstreet jeans.

The Fitz..  © UKC Gear
The Fitz..
© UKC Gear

... and the Mercury  © UKC Gear
... and the Mercury
© UKC Gear

We reviewed the previous iteration of the Mercury jeans back in 2018, which used cotton rather than the updated EcoMORPH Denim. 

Freedom of Movement

The freedom of movement in the 3RD ROCK jeans is really impressive. The material is so stretchy and they have the biggest diamond-shaped panel on the crotch that I've ever seen, making them a pleasure to climb in. They're not quite as free as a pair of loose fitting cotton trousers but they are exceptional for jeans.

Whilst both the Fitz and Mercury are a very tight fit, the Mercury is a slim fit from top to bottom. Every time I put them on I think 'these can't be flexible' but they really are!

No issues with getting a high foot in the Fitz  © UKC Gear
No issues with getting a high foot in the Fitz
© UKC Gear

The Fitz are very stretchy overall  © UKC Gear
The Fitz are very stretchy overall
© UKC Gear


I have both jeans in a 30 waist and 32 leg yet they fit very differently.

The carrot shape of the Fitz means that they're wider at the top and then taper down to drainpipe-size at the bottom. This means that they're roomy around the crotch and upper thigh but they're really quite tight from the lower thigh down. I'm more like a 31 waist in reality, which is a size the 3RD ROCK jeans aren't available in, but the Fitz fit just fine on waist. 

Figure-hugging Fitz jeans  © UKC Gear
Figure-hugging Fitz jeans
© UKC Gear

The Mercury are slim the whole way but they don't feel as tight as the lower part of the Fitz do. As they're consistently slim they are tight around the crotch and the 30 waist is only just big enough for me. If I was getting them again I'd go for a 32.


The jeans are made from 3RD ROCK's EcoMORPH Denim which is extremely stretchy and has that lovely rich denim colour (86% Organic Cotton 11% Polyester 3% Elastane 4 way stretch EcoMORPH denim for the Fitz and 80% Organic Cotton 16.5% Recycled PET 3.5% Recycled Elastane 4 Way Stretch EcoMORPH 2.0 Denim for the Mercury). 

The material is really nice and to the touch and the eye and I expect it to last a long time. All the stitching is beautifully done and they're both really well-made pairs of jeans.

It still blows my mind that the Mercury are so flexible despite being so skinny  © UKC Gear
It still blows my mind that the Mercury are so flexible despite being so skinny
© UKC Gear

The denim feels just like highstreet denim and is (apart from the stretch) pretty much indisernable. Both the Fitz and Mercury are a great choice of climbing legwear in the winter as the denim is nice and warm as well as being abraision-resistant. 

Eco-friendly credentials

As always 3RD ROCK are hot on their eco-friendliness and their jeans are no exceptions. The EcoMORPH Denim is made from organic cotton and uses a special processing method for washing and finishing the clothing that eliminates the major environmental issues usually involved in processing denim. You can read more about it here.

Fastening and features

Both pairs of jeans fasten with a single button, have belt loops and a zipped fly. There's two front pockets and two large back pockets. This is everything you'd expect from a pair of jeans and I can't see them bagging out as they're so tight!


Again the Fitz and Mercury differ here. I have to say that the Fitz look strange on me - they just don't suit me. That said, due to the unique carrot shape perhaps they just don't fit my legs. They seem to get lots of positive reviews on the 3RD ROCK site so I assume they work for most people.

The Mercury are just as stylish as a highstreet pair of jeans  © UKC Gear
The Mercury are just as stylish as a highstreet pair of jeans
© UKC Gear

The Mercury, however, are a different story. They look just like a regular black pair of slim jeans but you can actually climb in them. I really, really like them and they're my go-to pair of climbing trousers. Sometimes I even wear them when I want to look smart and I'm not climbing!


The 3RD ROCK jeans, and the EcoMORPH denim, are impressive not only for how incredibly stretchy they are but also because of their eco-credentials. Of the two models I've used I much prefer the Mercury, as they are a more conventional fit and appearance which suit me, whereas the Fitz are unique. Which pair is best for you is down to personal preference but the fit is worth a consideration before you buy. Either way they're the most impressive climbing jeans I've worn.

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