Originally LANs were built using a rather thick variety of coaxial cable. Later, when a thinner version was adopted, the original was colloquially referred to as thicknet and the later variety as thinnet.
A cross-section through thicknet looks more or less as one would expect.
Nobody can deny the inherent beauty in such cables.
As always a sense of scale might be useful.
A more realistic comparison is one with related cables.
Next to the thicknet is an example that looks like thinnet. This example is RG-59B/U. Real thinnet looks very similar, but has an impedance of 50Ω, compared to the 75Ω of RG59B/U.
The white coax is RG-6/U - commonly used to connect antennas and satellite dishes to TV sets.
The final cable is Cat 5e UTP - commonly used in current network installations.