I own two pairs of over-ear closed headphones, Audio-Technica M50 and SHURE SRH-440, they are both great.
The SRH-440’s are really comfortable, especially after changing the the pads to the SRH-840’s pads, but they are a little heavy and the pads are a little too shallow for my ears (my ears touch the inner plastic and it hurts after a while, a problem a lot of people seem to have). the shallowness of the pads is easily fixed with some bungee cord cut to length and shoved underneath the pads all around to give it a little more height.
The ATH-M50’s sound a little better, but their pads are a little small for me and not very soft. They are lighter than the SRH-440 so I can wear them for longer periods of time without feeling the band on top of my head, but the pads start to be uncomfortable after a while.

I decided to mount the 440’s pads onto the M50s, that way I could enjoy superior sound quality and prolonged comfort.
Luckily, the 440’s cups are a little larger than the M50’s, making the 440’s pads fit loosely on the M50’s. This was a big improvement, but the pads are a little too big, they slide all over the place and they could easily be knocked off the cups.
If only there was a way to make an adapter to make them fit… wait, I have a 3d printer!

The 440’s cups are elliptical while the M50’s are shaped like two distant halves of a circle with the tangents connecting them on the top and bottom.
After some quick measuring, sketching, and modeling I came up with a 3d model ready to be printed.
A few iterations later, we have the right scale and everything fits!
Now I can really enjoy my headphones.

This can be easily implemented for virtually any model of headphones (providing that the cups of the headphone that donated the pads are larger than those of the headphones on which they will be mounted)

The 3D printed model can be found on thingiverse