Koo Open Cube Sunglasses

The Koo Open3 (or 'Open Cube') are premium sunglasses from the maker of Kask helmets. With astonishingly clear optics and solid frames that stay where you put them, these are excellent shades – if you don't mind the price.

• Pros: Extremely clear optics, comfortable, pivoting arms can be useful for avoiding fogging, comes with tinted and clear lenses
• Cons: Not cheap

Koo is a relatively new brand of sports-focused sunglasses from the maker of Kask helmets. David tested the Koo Open glasses last year and they scored well. The Open Cube has the same large one-piece lens clipped into a solid, lightweight frame with novel pivoting arms, except it's a half-frame. The frame and lens wrap around the head very effectively to provide a lot of protection from sun and wind. The edges of the lens are well outside the field of vision; there's no annoying light coming round the edges in these and I never had a hint of dust or cold air bothering me.

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The most important aspect of any eyewear is the optical performance, so let's start there. The lens on the Koo Open Cubes is made by Carl Zeiss, and it's a very impressive bit of kit. There is not even the slightest hint of distortion right across the whole visual field. I tried these back-to-back with some mid-range sunglasses that I had to hand, and the difference was striking. I won't mention the brand of the other glasses, which sell for around £60-70, but the crystal-clear Koo lenses revealed those on the other glasses to be appallingly distorted. I don't think I could wear those other glasses again having seen what the view should look like through them!

The Koo lenses are very 'neutral', for want of a better word. Some other premium brands, especially Oakley, not only darken your surroundings but play with the contrast of the scene. If you put on a pair of Oakleys, the nature of what you are seeing seems to change and some features become more pronounced. Perhaps the best way I can describe it is to say that Oakleys make the scene 'pop'.

The Koo lenses, on the other hand, don't change anything. They simply make everything darker in a completely unobtrusive way. Nobody is second-guessing how you need the world to look; you're just seeing the world with more protection. Whether or not you prefer completely neutral sunglasses, or sunglasses that alter the scene to pick out certain details, is a choice you'll need to make for yourself. But I came to appreciate the understated and clean nature of the visual scene with these glasses.

Pivoting points

The other notable feature about the Koo Open Cube glasses is their rotating, pivoting arms. As you can see from the photographs here, these roll back instead of folding. There are multiple detants, meaning the arms can click solidly into several positions between fully open and fully closed.

While this pivoting mechanism might seem a bit of a gimmick at first, it did prove useful. One of the helmets I wore when testing these lenses came down quite low on the forehead, and touched the top of the glasses. Thanks to the detants, I was able to roll the front part of the glasses down one notch and thereby get the glasses sitting comfortably on my head without having to move the arms from where they naturally wanted to sit on my ears. (It's not me in the pics, by the way.)

I tested the Koo Open Cube glasses on a lot of bike rides, and also threw them into my kit when I went on a skiing trip. They performed incredibly well every time I wore them and they were a pleasure to wear. The skiing trip was a particularly good test, as the conditions were more demanding than on most bike rides. The excellent optics made the Koo glasses a delight to ski in, and the lack of any distortion across the entire visual field was really notable when having to read small details in the snow.

Ventilation

The lenses on this model have ventilation notches at the sides and across the top. Despite the lenses sitting quite close to the face, the ventilation seemed to work well. The only times I experienced any fogging at all was when I got very hot on a cold day and then stopped moving.

For example, the first time I wore these glasses was a sunny day with temperatures of minus 5. I did some hard interval repeats and found that, when I then stopped at a traffic light, a little fogging started to appear at the top of the lenses. But I have to stress this was only when I stopped; the instant I started moving again the lenses cleared right up. I couldn't get these to fog when moving at all. If only we could say that about all sunglasses.

Nose fit

Another neat feature of the Open Cubes is that the nosepiece flaps click back and forth between two positions, which means you can set them for a wide or narrow nose and then forget about them. I might have preferred it had these clicked between three or four positions, instead of two, to make the fit even more customisable, but this is a very minor gripe.

The solid rubber nosepiece, combined with unobtrusive grippers on the insides of the arms, mean the Open Cube glasses stay put really well over bumpy surfaces without any undue pressure on the head. A good fit is further helped by the specs coming in two sizes, each in standard shape or a shape optimised for Asian fit.

Lens choice

The lenses are interchangeable, and snap off simply by holding one outside edge of the lens and pulling the frame away. As with all sunglasses, this was a slightly nervy process the first time, but it proved to be very easy actually.

A range of replacement lenses are available and seem to be around £55 at the time of writing. Searching online reveals there is also a photochromic lens available, which might be particularly attractive for changeable conditions.

Value

The Koo Open Cube is unashamedly pitched at the premium end of the market and so is in competition with other high-end brands such as Oakley and POC. If you're in the market for sunglasses in this bracket, how they look is likely to be important to you. But I'd suggest you also pay attention to the nature of the optics.

As mentioned above, Oakley lenses make the world 'pop', whereas the Koo lenses are neutral and real. This is a distinction I hadn't fully appreciated until I tried the Koo glasses and saw just what a difference the two optical approaches can make.

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Which approach you prefer is going to be a very subjective thing, so in an ideal world I'd suggest trying various brands back-to-back to see what feels right to you. But having tried these for several weeks I remain very impressed and would cheerfully wear these all day.

Verdict

Amazingly clear optics and great protection at a premium price