[lindrone]

Ultimate Ears posted a video a couple of years ago (the video is dated 2009) showing people how they make each and every custom IEMs. I didn't know this video existed until today, when Logitech re-posted the video to their Twitter account. It's a good in depth look at the various steps involved in making custom IEMs.
 
http://www.youtube.com/watch?v=JWdwikZoXzA