Do materials alter frequencies and speed?

Resurrecting another dead thread?      Yes, the materials used in any cable’s (or PCB laminate’s) dielectrics affect signal transmission speeds, according to the Dielectric Coefficient (Dk) of the material. ie: https://www.edn.com/rule-of-thumb-3-signal-speed-on-an-interconnect/    and:  https://electronics.stackexchange.com/questions/494977/signal-velocity-in-pcb-traces          Feel free to argue (with those established facts).

Duelund 12 awg inserted in the doughnut hole of multiple Fruit Loops, and then the whole thing wrapped in a large-diameter cotton covering, is also quite effective.

l like PURIST copper cables they sound open,airy,great stage and bass impact.I am also using there phono cable for my TW phono stage with great results.This great sound depends on the copper used and the manufacturing method.