BentSk8r
Member
That's one of the questions I asked him at the time.
It is the Radical Design solo racer.
He slid it over the seat, on top of the Ventist pad so it looks easy to put on and take off.
I think it is this one (but I'm not sure if it was the narrow or wide version):
Bought those Radical Design solo racer panniers ten years ago to put on my Fujin SL II carbon seat. They do indeed just slip on and off easily and are the narrow version, though at the time I think there was just the one version.