No worries CDnum

Perhaps you can alter the thread title
to "silk inlay" to assist other students of these.?
GB stamps come under the general description
of "Dickinson paper" but I am not aware of
Bavaria, whether they used this paper
or not, the two look vastly different.
Dickinson Paper:
Named after its inventor, this paper, used for the Mulready and other envelopes, and in rare cases for adhesive stamps, has continuous silk threads embedded in it. A device intended as an obstacle to counterfeiters.
PS: Agree with Puzz, nice to see the thread isolated
and illustrated in your example.