Welcome to fusionaudio
To be more specific, the copper foils are insulated to protect against oxidation, then surrounded by air. The silver foils are not insulated. After having the cable for several years there is no deterioration in performance. The housing is also air tight so oxidation would be limited anyway.
I have two series, the Romance series which is of course romantic and lush sounding with richness and texture. Then I have the regular Fusion Cables like the Enchanter which is a foil based cable that will sound liquid and extended.
The conductor in the cable is sheilded by air and need strong protection. This is why cables are thick and a little stiff.