When glass caskets came out to the market, it didn't necessarily have anything new aside from the lid being made of glass. But the marketers of that time wanted to take the opportunity of highlighting certain design elements of the glass casket and blowing it out of proportion, claiming that it would preserve the flesh and bone of your deceased such that it won't rot or decay. These were incredibly absurd claims and it's ridiculous to think that covering a corpse in a tightly sealed container would prevent its decay. Still though, they sold the idea and some shares of these glass casket companies to people, which forced states like Louisiana to pass laws protecting consumers from fraud.
(Image credit: Fred Hunter/Corning Museum of Glass)