I have a closca loop helmet, which is also collapsible (not inflatable) and fits nicely in a backpack.
I presume it's not as light as an inflatable helmet, but it feels like a normal helmet, costs like a normal helmet, and I don't need a pump to use it.
I don't know if there are any other brands that make this but I'm super pleased with the concept. It lets me have a helmet in my backpack in situations where I wouldn't be carrying a helmet otherwise, for using with scooters and the like.
Oh interesting. Apologies, I've edited it now. It was working for me so I didn't notice.