Fascinating fact, couldn't resist posting
Plimsolls were made from Gutta percha, a non latex bendy material from a tree. It was over harvested in the 1850s and the supply chain broke down, which meant shoes had to be made from rubber. Gutta percha is not latex based like rubber as it comes from a different genus of plant. It is used for medical purposes now. This is probably the origin of the word Gutties.