A unique type of earbud
made by Koss
that incorporates earplug
They have a slender tubes protruding from the drivers, which go through the center of (almost) conical earplugs made of "specialty ear cushion material." The listener squishes the earplugs, inserts them into their ear, and holds them there for a while as the foam expands to the limits of the ear canal. This lets the listener block out ambient sound. The listener does not have to turn up the volume to hear their music in high noise settings.
They sound good. Nice bass.
They come with many replacement earplugs in an ugly blue change purse. The actual plugs may be a problem for some people. They fit just fine in my ears, but some people (close friends, to be sure), had trouble keeping them in their ears properly. If the earplugs are not completely in, the low end is lost.
They can be retrofitted to provide extra acoustic isolation, or better fit, by replacing the included foam bits with bona fide earplugs from your local drug store