For the reflective layer, gold, silver, or a silver alloy is typically used.
Generally, these metals are already resistant to environmental pollutant that could migrate through the disc with moisture. Gold is more stable and longer lasting but still, more expensive.
The data layer is an organic dye, which degrades over time. Disc makers have typically patented the organic dye they use for their discs so I am not sure if they add any special generic material to make them more durable.