We have been using some very long lived delrin  (as tested by my machine),

but it only comes in 1 mm thick sheets, so we have to machine it down.

The sheet is machined across the top of a 250  mm diameter fine saw blade,

and produces the following grades:

Plectra taper in width from 2.8 mm at the root, to 0.5 mm at the tip, over 10 mm length.

 

Pre-voiced plectra:

 

GREEN           treble and 4’

BLUE              mid/treble

BLACK           tenor/middle

RED                 bass

PLAIN  for hand cutting - zero net taper, yet a slight curve underneath.

 

Plain plectra:

Delrin sheet of thickness 0.5 mm is used for these.