Giro's new Aether helmet employs a shell-in-a-shell design that allows them to move independently of each other thanks to a ball socket and elastomer joint system called MIPS Spherical. Because of this, the outer shell can float ever so slightly on top of the inner shell, which allows it to take in and dissipate rotational impacts better than a traditional design. It also means that there's no need for the plastic MIPS liner.
The Aether is quite light - Giro says 250-grams for a medium - and retails for $325 USD.
While there's no official, industry-wide standard when it comes to MIPS, the very large majority of performance helmets have adopted the plastic inner liner as it's said to let the helmet to 'slip' on the rider's head during certain types of impacts. That slip is claimed to go a long way in preventing certain types of head injuries because it allows the helmet to move slightly and absorb some of the critical forces. But the MIPS liner isn't a slam dunk, with it messing up the venting and fit of some helmets, or allowing the helmet to slip and rock around when it should sit still.
MIPS Spherical, which was a co-development between Giro and MIPS, aims to solve those issues while still offering all the same benefits.
With no MIPS liner to block the vents, the Aether looks extremely airy.
The Aether itself has been a three-year project, with the MIPS Spherical system first being used in a snow helmet where it was easier to apply. Cross-country and road helmets, with their immense amount of venting, are a much more complicated application, hence the long development time.
One of the challenges was that the complicated shell shape was preventing Giro's normal EPS foam from getting into all the tight spaces that it needed to fill. The solution was to use an EPS foam with smaller beads - Giro calls it Nano Bead - but this turned out to be a win-win as it then allowed for the inner and outer EPS shells to have a different density, and therefore be focused on different types of impacts. Nano Bead is softer, so it's better at dealing with slow-speed impacts, whereas the hard EPS shell can take in harder hits.
Venting aside, the Aether looks a lot like a traditional helmet, and its outer dimensions are no larger, either.
If you're thinking that this shell-in-a-shell design sounds familiar, it might be because you've seen it before from 6D and Leatt. Both other those options are relatively heavy compared to a standard lid, as well as looking absolutely huge on a rider's head. And that's why I expected the Aether to have the same mushroom-like shape... But it doesn't. In fact, it has essentially the same silhouette as the less expensive Synthe that uses the standard MIPS liner. It's even the same weight, too.
One thing that is different is the temperature of the rider's head while wearing the Aether - Giro says that they've measured both and the Aether can lower temps by 2-degrees compared to the Synthe. That's a big deal if you struggle in hot weather like me, or live somewhere that often feels like it's the inside of the volcano.