Corded ear plugs are convenient if you have a process that generates noise intermittently--they can be taken out and hung around your neck, then reinserted as needed.
There are four categories of ear plugs:
Which are worn once and then replaced when workers reenter a noise area
Which can be used repeatedly and cleaned with soap and water
BANDED EAR PLUGS:
Which essentially are two foam ear plugs held together by a plastic or metal band
DETECTABLE EAR PLUGS: Which can be used in environments where you need to be able to screen for foreign substances in the finished product.