You can read about it in different manufacturing sites, eg. Yaxi, Dekoni etc.

Just one example: https://dekoniaudio.com/articles/so-you-want-some-focal-measurements-with-the-dekoni-audio-ear-pads/

When interested in experiencing even subtile changes: Cut out rounds from coffee filters and put in your cans … you’ll be astonished how noticeable the differences are.

Headphones Show did a pretty good video overview of how pads affect sound. Link to it - https://youtu.be/pPcMxmwDw-c

Thanks, this is some good info!

Good video, Thanks!

Speakers and headphones are very similar in nature. Just like how a room can really influence the sound of a speaker, similarly the pads on headphones can have huge impact on the sound signature of a headphone. A pad after all is the "room" for the headphone driver.

Density of the material (velour, leather/sheepskin/lambskin, suede) plays a major role here. Higher density materials tend to absorb the high frequency, hence elevating the bass. Materials like leather/sheepskin/lambskin and suede are of higher density and are usually used to increase the bass response of the headphone, pushing towards a warmer sounding headphone. However, materials like velour and any sort of fenestration in leather pads are of lower density and have emphasis on the higher frequencies. Bass is not as elevated as the leather or suede pads.

Density of the memory foam plays a role in increasing the soundstage. If the stock pad was less thick than the aftermarket pad, then you will observe a perceived increase in the soundstage, as the headphone driver is further away from your ears.

These are my generic set of observations, and of course YMMV based on headphones. It is wise to read the frequency response graph for each pad-headphone combination. Folks from Dekoni Audio do a great job of measuring their pads, plus their pads are of great quality too!

This was a good read with lots of nice info, Thank you!