Amel confirmed the material used is PU (polyurethane). They added that the hardness is 90 shore. It is 5 mm thick
As many A54 owners know, the original material does not last long. I replaced mine
2 years ago with Tufnol (phenolic laminated).
Hope it helps
Attika A54 #117
Attika A54 117
Paraty - Brazil