@ Bobby: I don't know. Probably the stretched foam.
@ Masonspappy: as long as you name each node according to what it does, it's pretty good to read. Naming is crucial!!! If you just have a hundred standard nodes, you have to interpret the whole line, which is much harder.
@ Nils: I had displacement in the foam in my earlier attempt, but placed a RT-reflective shader after it, which caused the long render time. So I dumped the displacement and put the reflective before the foam (and added another non-RT after). Much faster. But I have to add some displacement again, you're right.
2 more versions as tests. Got something better than this brewing....