To me it looks like rubber, this particular strap.
But Patek calls it composite as it sounds very posh, eeeeaaarrr! ;-) !
A sharp scalpel should be the best way to cut through it.
One can call it also composite, as rubber is a composition of materials, but the term composite is more used for hard, none flexible materials, mostly bonded together with resin.
I did not have the pleasure to adjust the 5167 strap, but I reckon a little DIY is not too risky ...
Regards
Moritz
This message has been edited by COUNT DE MONET on 2010-08-06 09:19:03