Thanks all for the answers! It's both the surface and the feel of the paper that I like. The thin-ness is a big part, but it just looks cool. Art300 is kinda close and I do like it, but it's more textured and very thick in comparison. I don't think most of these are foldable. Some have creases from how they were stored.
I'll admit that once I found Ilford paper in the late 90s that I never really looked around at others. I've tried a few sheets of Bergger because someone gave me a sample pack, but that's it.

Yes, there should be a "history of photographic papers" somewhere. Every detail of film is written up in countless places; did anyone do that for paper?