Well, nothing special. But very useful and comfortable.
On my Bench I had some "Howard Leight L2" Earmuffs, which have around SNR=-31dB noise cancelling properties. They are very comfortable, at least on my head.
I always wanted to have headphones which are very private in both directions. Additionally they need to be comfortable !
So I opened them, removed the dampening foam inside, drilled a 5.5 mm hole into it and glued in a stereo jack.
Then I took some old, cheap and ugly "Bosch" headphones which were handed out during an intercontinental flight, removed all but the speakers themself and hot glued them inside the earmuffs.
The cable from L to R was fed through two 2mm holes drilled into the housings.
Layed on the foam again and mounted all together again.
Et Voila !
The stereo cable is removable and I do not think that dampening was deteriorated because of the modification (at least I cannot feel it louder than before).
Enjoy this project?