The basics of coaxial cables
The coaxial cable consists of three parts: the center conductor, the dielectric material layer and the shielding layer. The center conductor is in the middle of the coaxial cable, which can be solid or stranded. Surrounding the center conductor is a dielectric layer, which acts as a sort of buffer and holds the center conductor in place. Outside the dielectric layer is the shielding layer of the coaxial cable, usually copper foil, aluminum foil, braided mesh or a combination of the above. Then isolate the shield from the environment with something like polyvinyl chloride (PVC).
RG-8, RG-9, RG-11 impedance are 50Ω, used for thick cable Ethernet
RG-58, impedance 50Ω, for thin cable Ethernet
RG-59, RG-75 impedance is 75Ω, used in TV system
RG-62, impedance 93Ω, used for ARCnet network and IBM 3270 network