The filter fits into my left ear based on a mold. It’s flesh-colored and visible when my head is viewed directly from the side. Otherwise, it can’t really be seen. It has holes in it but I don’t know its internal design. It was made almost 20 years ago, so I’m sure the state of the art has changed.
The filter limits unhelpful input into my left ear, which for me is conflicting input in voice range and high-pitched loud noises.
I was instructed to wear it for classes and meetings and to sit to the left of the main speaker when possible.
I haven’t worn it in years, but I credit it with a higher GPA and a few friendships that might have struggled to form if I hadn’t been able to hear well enough to converse.