[critofur]

I have two pairs of basically the same headphone except one has pleather pads and the other has velour pads.
 
I know people have said that the velour pads give you a little less bass, and make the headphones sound a little more like "open" headphones, and reduce noise isolation.
 
But the degree to which noise isolation is reduced is well beyond what I would have guessed from the descriptions and reviews I've read - the extent to which I can hear people and sounds around me, while wearing the phones with the velour pads is more like  to NOT WEARING headphones than like wearing the pleather pad headphones.
 
And, of course, as many people have mentioned, the headphones with velour pads "leak" sound a lot more.  My kids said "I can hear what your listening to from here! (across the room) - they thought it was remarkable how loud the music sounded compared to when I was listening to the other headphones.

 

[zazex]

  I have two pairs of basically the same headphone except one has pleather pads and the other has velour pads.
 
I know people have said that the velour pads give you a little less bass, and make the headphones sound a little more like "open" headphones, and reduce noise isolation.
 
But the degree to which noise isolation is reduced is well beyond what I would have guessed from the descriptions and reviews I've read - the extent to which I can hear people and sounds around me, while wearing the phones with the velour pads is more like  to NOT WEARING headphones than like wearing the pleather pad headphones.
 
And, of course, as many people have mentioned, the headphones with velour pads "leak" sound a lot more.  My kids said "I can hear what your listening to from here! (across the room) - they thought it was remarkable how loud the music sounded compared to when I was listening to the other headphones.

 
 
The size of the earcups and the clamping force will affect this as well.

 

[hekeli]

Pointless discussion without specific models. Even similar pads can be very different (f.e. DT770 velour vs DT990 velour pads). There can be holes etc.
 
On Superlux HD-330 I measured 770 velours having better isolation than AKG 240 pleathers. The velours have a tighter fit/seal on head.