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.
SINGLE USE EAR PLUGS:
Single-use, or disposable, ear plugs are the most common type used today. They are popular because of their low cost, ease of use, and high level of comfort. There are different styles, ranging from the almost 50-year-old yellow PVC barrel ear plugs to the latest contoured polyurethane (PU) foam ear plugs.
PU plugs are soft, comfortable, easy to roll down for insertion, and available in a variety of different shapes, sizes, and colors. PU foam is also made in different densities, which means you can get a heavier ear plug that blocks out the maximum amount of noise (NRR 33 is the current max) or a lower density in a smaller shape that exerts less pressure on the ear canal. These are particularly useful for people who wear ear plugs for extended periods of time or have smaller ear canals.