I've had my 325s for years (the original 325) but mostly preferred speakers. My wife has been complaining that I always have music on, so I thought I'd kill two birds and use my headphones more often. Love the sound but could never get comfortable with the earpads. I've tried:
Sock mod - not just covering the bowls, but a wool sock rolled up into the size of a large earpad. Very comfortable but the soundstage was slightly muffled.
Bowl tape mod - used 3/4" velcro strip wrapped twice. Looks great and increases the bass, but not more comfortable.
Speaker grill cloth - takes the shine off the highs of the original 325s.
Rat shack flats - Very comfortable but the material muffled the highs too much, the quarter size hole mod still left too much material, and they put the cans too close to my ear, reducing the soundstage.
So I ended up with the ultra rat shack mod. Rat shack flat pads with a large hole (40mm - the same size as the other side), with a donut shaped spacer covered with speaker grill material for looks and sound.
The cut on the pad doesn't have to be real clean as I use that side towards the cans. The donut could be any rigid material but I used a soft, cork-like material for comfort. The size is 5mm thick with a 40mm id and 60mm od. And the speaker grill material is wrapped around the donut and glued on the back side. The donut is just inserted into the pad and then the pad is attached like normal.
Clean look and nice shape and comfortable enough to wear for hours.