Sounds like a UV curing acrylic (or other polymer) is put inside a silicone cover. Neat idea but the housings do look weird. I'd rather have a separate 'fit' kit and differently shaped housings. The ear pieces and the UV led with a wired trigger/button. Place the earpiece in the ear and press a button for X seconds, then swap tips and repeat on the other side. Plus this would remove extra one time use stuff from the TWS. They could even sell replacement tips.