The Shure pads are slightly larger in outer circumference, slightly smaller in inner circumference, and slightly thinner than the stock pads but the sponge material isn't as soft so it doesn't squish as much as the stock pads.
I decided to do this in the first place because:
1. In my experience, the inner side of earpads needs to always be stiff and smooth. Being too soft dampens the sound without any benefit, only detriment. Texture and wrinkles hurt the bass and soundstaging, they also hurt the treble and midrange to a lesser extent.
2. I had the pads on hand already. =p
I speculate that texture/wrinkles affect the air flow much like the earth's friction with the atmosphere cripples a hurricane. Softness causes loss in clarity and detail, and soundstaging suffers as well; I imagine the reason why is because of energy from the sound being absorbed.
The Shure pads have a more firm and smooth inner side, that is why the sound improves.
Back when I had T50RP, I stiffened the inner side of the earpads with six coats of plasti-dip to achieve similar results. Same with MDR-7509HD and V700DJ, 7509 showed the most drastic improvement in sound. I would do it to my other headphones, but none of them need it or I simply cannot do it to some them like DTX501 or my modified Momentum On-Ear because the inner side is a breathable fabric rather than solid pleather, so coating them would muffle and kill the sound.
When I had IEMs, I would stiffen the eartip tubes with plasti-dip, which would give similar improvements as well.