Perhaps the manufacturer thinks that the meaningful rating is the
breakdown voltage that can be attained with the material when it is
properly applied.
Since that "proper application" would include some minimum thickness,
you're left with a voltage.
This, in turn, means that if you're intending to do some application that
_doesn't_ conform (as it were) to this minimum thickness, then you're
either (a) smarter than the manufacturer, or (b) dumber than the
manufacturer. It's always hard to tell which in these cases, because the
stuff has probably been in production since 1953, and all the folks that
actually knew did the math on it are dust.
You could try calling them up and asking how many coats you need to get a
withstanding voltage of whatever it is you're looking for. Sometimes
that'll prompt a response from someone who actually understands what's
going on and why, sometimes that just gets you shrugs (or worse, some
idiot sales man telling you what he thinks you want to hear so he can
sell you a case of the stuff).
Asking "could you recommend a competitor who's actually competent" will
piss them off, but might make you feel better.
