Need modding advice for sound-leaking headphones

[Zero55]

Good day to all.
 
I usually don't ask for help on forums, but this time I want to solve problem with solid advices, which I hope, I will get from experienced people.
 
I have some overear headphones, while the sound is ok there is another problem. No isolation for sound leak whatsoever. I opened right earphone, and there is just speaker, with some thin sponge over the metallic net(placed on the outside of earphone), which in situations where i would like to turn up the volume, sound leaks and earphones act in manner of small speaker with low sound, low but very recognizable.
 
I really like those headphones but i don't want to be moron walking around and imposing death metal music to any person that walks by me.
 
At this moment I really don't have anything that I could try to stuff in the earphones to isolate sound from leaking.
 
 
I would like to get advice on how to fix that leakage - is there some specific type of sponge or maybe some better material that would help. Maybe my aproach is wrong, maybe i can solve it on some smarter way.
 
Forum, what's your opinion on this?

 

[linglingjr]

 Maybe my aproach is wrong, maybe i can solve it on some smarter way.

The right thing to do would be buying closed back headphones.  Trying to mod an open headphone will make it sound terrible as the driver wasn't designed to work in that environment.  
 
I'd look into buying a closed can.