rubber and a clear seal. rubber for the buttons seal for the face etc...

A good water proof watch such as a divers watch has a rubber gasket under the back of the watch and they also have a threaded crown. Usually one like this costs several hunred dollars. Also when you want to have the battery changed. You should send it into the company that made it, because most jewlers dont' have the ability to properly seal the watch up the way it was when you purchased it.