I’m currently flying in a twin engined jetliner and have some impressions regarding isolation.
Etymotic HF5 with custom molded silicone sleeves - these let me forget that I’m on a plane, I can barely hear the engines, let alone my fellow passengers. I listened to a Sibelius violin concerto and didn’t have to crank the volume at all. Sadly, they became uncomfortable after a couple of hours and I had to take them out.
HF5 with medium triple flange tips - these don’t isolate as well as the custom sleeves, I can still hear everything but it’s dramatically attenuated.
HF5 with Shure olive foam tips - these just don’t fit my right ear well. On the left ear, they seemed to isolate very well though. And they’re definitely way more comfortable than the triple flanges.
Revonext QT2 with Spinfit CP145 tips - these IEMs are vented and just don’t isolate as well as the Etymotics. That said, I can tell that I’m getting a good seal from the Spinfits and they still attenuate the volume somewhat. I’m finding myself listening at higher than normal volumes, though probably only about 5-10 dB higher, which isn’t too bad. Comfort is very good.