In order to prevent water molecules into the movement inside the apron installed, usually at the bottom of the back cover, and some inside the crown also exists. General use of rubber material, some watches with nylon material.
Waterproof aprons are also called "O" rings, which are due to the fact that they are round in most cases. In addition, there are other shapes such as square, oval, and some square water proof The apron , which in fact is also circular in the free state, has also formed its existing square by shaping.
Different watch waterproof apron life is different, usually within the specified time will have to change, in order to prevent the apron aging watch waterproofing performance.