Today when I was visiting the marketplace for some new pots, I came across a merchant selling these odd, a bit fabric-like white sheets. He told me that the Egyptians make these from reeds to write on them.
Personally, I don’t see a need for such a material. Just use a clay tablet like a normal person!
If I wanted people reading my words millennia from now, I’d chisel them into stones. My communications are private. Get with the times, grandpa!
Then soak your tablets after writing them!