Other reviews have already offered a wealth of useful information, so I'll just share my own opinion, based on a comparison to my previous wireless earbuds (the kind with a neckband). Because I have extremely narrow/curved ear canals, I had written a CSR ahead of time to inquire about the bore diameter through which sound is transferred. The CSR said that the bore was 3mm, but when I got the goods, it was really 5mm! > Fortunately, the smallest silicone sleeve fits well enough and provides a decent seal. Unless I really twist it in deep, it hangs outward at an angle, which makes it seem a little funny.