I honestly do not know.
Whilst burning-in, they do not sound as loud as the Superlux or JVC sitting next to them.
Sound isolation is not a priority, at all, for my choices and there is no one around to hear sound leakage.
Performing a simple 'clamp the two cups together' reveals little leakage compared to the JVC or SL's when playing Toccata and Fugue.
But, again, I don't value lack of leakage so do not know what would or would not be acceptable to you.