revised pic on that URL
the Philips 373 MKT was polyester as was the yellow TC probably, by that
flame test.
Yellow flame , sustained after flame removal, no drips, slow
progress,brittle remains, although HCl not smelled.
This film 15 microns, WVTR permeability of 25 micron films in g/m^2/day
polyester 4
Polythene 20
Polycarbonate 170, I didn;t realise this was so "porous"
From the boating industry epoxy has much better permeability figure than
polyester.

Now just to find the quantative deleterious effect of water/vapour on
dielectric strength.