In-Ear headphones (also known as in-ear monitors, or IEMs) are earbuds that are inserted directly into the ear canal. In-Ear headphones offer portability similar to earbuds, and also act as earplugs to block out environmental noise. There are two main types of IEMs: universal and custom. Universal In-Ear headphones provide one or more stock sleeve size(s) to fit various ear canals, which are commonly made out of silicone rubber, elastomer, or foam, for noise isolation. Universal canalphones are typically marketed to casual listeners and are relatively inexpensive, though some offer very high audio quality.
Custom In-Ear headphones are fitted to individuals. Castings of the ear canals are made, usually by an audiologist. The manufacturer uses the castings to create custom-molded silicone rubber or elastomer plugs that provide added comfort and noise isolation. Because of the individualized labor involved, custom IEMs are more expensive than universal IEM
