During the '80s and the '90s, a lot of media cases were made of thermoformed PVC. I believe this trend was created by Disney and Blackbourn with their VHS cases. Then with DVDs, industrial standards for media casing have changed in favor of injection moulded PP.
For example, the latest Neo Geo AES cases are made of PP plastic but early Neo Geo AES cases were completely different. Internal trays were clearly made through thermoforming, as they have strong light reflection properties, but I'm not sure how external cases were made. They give the impression of being made of leather but are certainly some kind of plastic imitation. How were the external cases processed? Is it also PVC?