Wood wool - Wikipedia
https://en.wikipedia.org/wiki/Wood_wool
Wood wool, known primarily as excelsior in North America, is a product made of wood slivers cut from logs and is mainly used in packaging, for cooling pads in home evaporative cooling systems known as swamp coolers, for erosion control mats, and as a raw material for ... in hutches and in cardboard boxes when shipping day-old poultry within the ...
Terminology · Grades and classifications · Applications · Properties
This is what I have found in several original untouched doors and you can still get it. It looks like the stuff that is frequently used as a soil mat in freshly dug ditches. why not use the the original stuff? But I would put some penetrating sealer on it first.