The flexible joint material I believe Dick Merchant refers to is soft
buckskin.  Warning: Not all buckskin works.  Some buckskin is tanned
hard, for shoe soles and such, I guess.  I have some that would make
shoe soles.  But felt punchings also work well, using thick hot hide
glue.  Watch out that the glue doesn't soak into the pad, because that
will stiffen it and really stop the piano's ability to pump easily,
even though it's tight, again.

Craig Brougher