Hyundai explains in a press release that there was concern passengers' heads and limbs could end up going through the big glass opening in a rollover, leading to serious injury. The resulting airbag design aims to prevent that by deploying when a rollover is detected to contain occupants' bodies. It inflates from the back of the sunroof toward the front in 0.08 seconds and will go off regardless of whether the sunroof is open or closed.
Hyundai, which together with Kia and Genesis had six of the 15 recent IIHS Top Safety Pick+ vehicles, claims the airbag reduced life-threatening injuries to minor ones during testing. It also noted that the company has 11 patents on the technology. No mention of when these airbags would appear in production vehicles was made. We would imagine that whenever Hyundai starts offering the feature, it will show up first on high-end vehicles such as Genesis luxury cars.