Plumetty is a fur, evidently a variant of the vair furs; it is made up of panes resembling feathers. Visually, it’s similar to a lozengy field, and its tinctures are blazoned the same way. Plumetty is a period field, found in the arms of Mydlam, c.1460 [RH].
The interior details of the feathers are diapering, and are considered artistic license. When no internal details are shown, plumetty becomes very close to a form of papellony. See also field treatment.
Duncan Brock of Greyfeather bears: Plumetty argent and sable, on a fess purpure a brock statant argent.
Damian Papyngeye bears: Plumetty argent and vert, a popinjay purpure.