Testing various headphones, it's not uncommon to see many different types of earpads, some compatible with each other. From beyerdynamic, the DT880 uses smooth velvet earpads, while the DT440 uses velour; in addition, there are vinyl earpads sold separately by beyerdynamic that are compatible.
While it is easy to imagine how the earpads might change the shape and the feel when worn, I was curious as to what effect the earpads would have on sound. So, I decided to test the frequency response on the same set of headphones while swapping the earpads.
The DT440 was used for testing, and the earpads from DT880 (velvet), DT440 (velour) and the vinyl earpads (sold separately) were tested.
From the left, vinyl, velvet, and velour earpads
Vinyl, front side
Vinyl, rear side
Velvet, front side
Velvet, rear side
Velour, front side
Velour, rear side
Red: DT440 - Velour
Green: DT880 - Velvet
Blue: Sold separately - Vinyl
The velour and velvet earpads were nearly identical in sound, while the vinyl earpads relatively emphasized the bass and the midrange. This is likely due to the vinyl being more airtight and the pad not having breathing holes in the rear.
If the headphones are well-balanced, the velvet pads are recommended, while you might want to try the vinyl pads if you find that the bass could use some boost.