Purchased the fenestrated sheepskin variant. Had these for about 4 years now and they are holding up great. The cushioning seems denser than the stock pads and is holding it's shape much longer than the stock pads did.
Comfy but Hybrid Velour fell apart over time from sweat in one year.
I liked the comfort of the Hybrid Velour but unfortunately the fenestrated sheepskin ring came apart over time. A little less than a year after purchase. I suspect it probably was because I was sweating a lot due to being in a very hot climate with poor air conditioning. The earpads weren't exactly soaked but they would often be damp after a long day. Whatever glue they use to attach the fenestrated sheepskin to the adapter mount/inner ring must not hold up well to moisture/sweat over time. That is just my ignorant speculation though. Other than the sweat I tried to take care of them as best I could. If you live in a hot climate and/or tend to sweat a lot I would avoid using the hybrid velour & try the full sheepskin or fenestrated sheepskin instead. Or just get better air conditioning than me. :P I took one star off for being a bit expensive in my opinion and not being as durable long term as I would have liked.
I picked up the Fenestrated Sheepskin pads for my Sennheiser HD660s2 headphones. The sheepskin pads trap less heat and feel much softer on my head. These earpads made long listening sessions much more comfortable.
They are well built for the price. Was expecting a shiny velour finish like the originals but they're not bad. Gonna use them for when these get too worn.
One concern I do have is that they feel more squishy than the originals, which will affect the noise seal.
Worthy upgrade over the stock ear pads. The Fenestrated Sheepskin version is comfortable, breathable and doesn't impact the sound quality in a negative way in my opinion.