It takes a lot more than just that to really isolate. I use Remote Audio HN-7506: physical mass plays a part. Those are heavy, have gel earcups that are physically solid and bulky, and clamp really hard on your head. Earbuds aren't physically big enough and can't produce a rigid enough seal to compare… at least not AirPod style ones.
I've not worked with rigid, custom-molded in-ears. Something like that might be enough of a barrier, but remember if sound waves can physically move the earphone against the seal, that's going to be sound leakage. The Remote Audio cans aren't designed for comfort, they're designed to control sound pressures that'd instantly wreck your eardrums, like high-caliber nearby gunfire for extended periods. The headphone drivers are literally an afterthought, added by a separate company if I remember correctly.
