I received the polypropylene webbing today. The colour is an excellent, high-visibility yellow. However, it is much too soft for a cold-water harness. I'm thinking it would twist around a lot, hang limp, and be seriously hard to don. It's much like the straps on a typical, good quality gym bag.
That said, I would consider using it for the warm water travel bpw I'm assembling, as it would be more comfortable than stiff webbing if it were placed next to skin or over a thin rash guard.
Also, I told the folks at strapworks that I would be using the poly webbing for scuba, and they enclosed a note with my order saying that they did not recommend it for that application, and they included a 6" sample of their basic black nylon scuba webbing. It seems to be pretty standard stuff, maybe a bit softer than the harness that came with my Deep Sea Supply bpw setup, but not by much.
Looks like I'll have to try some of the stuff from northeastscubasupply.com for my cold water setup. Comes in lots of colours and is advertised as "stiff webbing", so hopefully it's what I'm looking for.