Non-custom earplugs are typically foam material which tend to be disposable or silicone which may be reusable. Earplugs sold in the U.S. are required by the U.S. Environmental Protection Agency (EPA) to have a noise reduction rating (NRR),which is an estimate of the reduction of noise at the ear when protectors are worn properly. However, due to user error the actual noise reduction is often much lower than listed. This is why it is so important to understand the intensity of noise you are exposed to and protect yourself appropriately. If you are unsure, it is better to wear both earplugs and earmuffs.