https://www.audioreviews.org/guide-to-iem-silicone-eartips/#E
EarrBond EBT New Hybrid Design Eartips with Metal Core (CU) Copper
Bore size: regular, with copper insert
Stem length: regular
Feel: soft with semi-firm core
Bass: 4.25
Midrange: 4.00
Treble: 4.00
Soundstage: 4.25
Vocal presence: 4.25
At US$50 for two pairs (mimimum order quantity is 2 pairs), these hybrid eartips are one of the most expensive eartips in my collection. Equally as comfortable as original EarrBond EBT eartips and
feels softer than Pentaconn COREIR Brass eartips. Isolation is exceptional. Are they worth US$25 a pair? Frankly, no! Performance is on par with silicone eartips such as Final Type E and Divinus Velvet. However, if you are looking for foam-level isolation with upper-midrange clarity, look no further. The difference between copper and stainless steel is copper eartips sound warmer and fuller. The vocals are more intimate also.
Safety concerns: Since the metal cores are inserted halfway into the nozzle. It may accidentally slipped out and leave inside the ear canal… Let’s say I am paranoid.