It sounds to me as if Bernt Damm needs stitched damper felt rather than
the more normally found flat variety.  For the sake of authenticity he
should replace with identical material if at all possible.

Backed and stitched damper felt is readily obtainable from Heckscher
and Co in London.  It can be had in two widths, 3/4 inch and 1. 3/4
inch, and either flat or tapered along the length.  You need to
guillotine the correct width off a strip that is long enough to recover
all relevant notes on the piano.  Their latest price list omits the
tapered variety so this may be no longer available.  The price is
around GBP 5 and GBP 8 for the two widths.

Heckscher and Co can be found at http://www.heckscher.co.uk/

Kind regards from Great Britain,
Nicholas Simons