I am familiar with "birch bark."
I have done caligraphy on sheets up to 12x18 inches.
It peels like parchment paper, thinner and thinner.
It was used by NE indians (USA) as the outside covering of canoes.

Like paper/parchment it could be easily folded into hats/caps.

Sincerely,
Gargoyle

One of the most wonderful aspects of the tree is a source for birch-sap beer.