The process is called ‘vulcanization’ and it is one of the major technical advancements that makes modern life possible as before vulcanized rubber it is was hard to water seal. You could do it with wood and tar but rubber gaskets are like magic.
[https://www.sciencedirect.com/topics/materials-science/vulcanization#:~:text=Vulcanization%20is%20a%20chemical%20process,viscosity%2C%20hardness%20and%20weather%20resistance](https://www.sciencedirect.com/topics/materials-science/vulcanization#:~:text=Vulcanization%20is%20a%20chemical%20process,viscosity%2C%20hardness%20and%20weather%20resistance).
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