in the case of rubbers of xt600, i'd describe this wear as compression & hardening. tube layers really helped to minimize sprocket/wheel free play, but feedback was still not enough pleasant.
red (kinda medium strength) polyurethane was lucky try, the feel is probably the same as of new rubbers and still in the great shape (no free play) after 2 years and lots of mileage (including 2up/travel load).

where did you get the red ones?

when looking for options, polyurethane was available mostly in form of rods.
this seemed to be hard way - not exact diameter, too much difficult cutting..

a friend works at pipeline maintenance, he was able to get a flat piece from pigging device - a segment of used cleaning circle. during cleaning of pipes, only circumference was worn, central part was fresh.

thickness (height) of that flat piece was almost the same (~28mm, don't recall exactly...) as of original rubbers (including that smaller "buttons" on the both sides). for the best results, still had to compensate difference with a shim next to sleeve.