Karl wrote
It turns out that I had a shielded ethernet cable lying around that needed its ends replaced (due to broken retention tabs), so I cut one of them off to take a look.
It was labeled as "ETL verified Cat.5e STP." The shielding is proper aluminum foil (not metalized plastic as I had thought), but it's 1/4th to 1/5th the thickness of kitchen foil (0.0002" on my micrometer vs. 0.0008-0.001"). It was wrapped around the entire 8-wire bundle (not the individual pairs) and was grounded at one end only.
OK, this is really embarrassing :( I misread my micrometer, and it's actually closer to 0.0012. So not too bad for shielding value.
(I was really tired when I took the original measurement, so I'm not sure how I goofed.