Bought these over two years ago for my 6XX's, purchased the Fenestrated Sheepskin finish but did not have any glue issues like some other reviewers. They've help up great and are probably my favorite pads for the Sennheiser lineup. Just as comfortable as the stock pads but more durable and run cooler. Haven't noticed a significant sound signature change. Might buy another set in case they do start falling apart but I won't hold my breath. Overall satisfied.
I liked the feel of the smooth velour on the original pads and the hybrid ones, but they would always make me warm and sweaty. This contributed to them getting dirty. So here I am buying a second replacement with fenestrated sheepskin now. It doesn't look crazy durable, so I don't expect them to last forever and a cheap replacement filter would have been a nice addition. Otherwise, good pads for a good price.
They do the job for about 6-8 months, and then they will start to completely fall apart. The inner lining is quite awful at staying together, and both have started to completely fall apart after just one year. These are just not OEM quality, they are far below that.
I have had two pairs of these and with both the glue has unstuck in a period of a couple of months. Fortunately, they can be glued back together, but having to fix a product after a couple of months does not bode well for its quality.
If you are okay with the knowledge that you will likely need to glue these back together then these are comfortable. It is unfortunate, however, that the stock pads lasted for a couple of years and the replacements are so much worse.
I got the fenestrated sheepskin, and while they are very comfortable, I can't recommend them as they have fallen apart after about a year of use twice in a row. The first time it happened I thought I was too rough on them when pulling them off the headphones, but I was very careful with them the second time. I have managed to glue it back together, but its not ideal. For the price, I am very disappointed. If I bought these a third time it would cost more than the 58x I bought them for
I bought the sheepskin variant hoping to fix a squeak problem that I've had with both my 6xx and 58x for years, and while it mitigated it, it didn't completely fix it. Imagine my surprise that right when the warranty period ended, the sheepskin on the inside detached from the back of the earcup. I had to superglue it back together and it hasn't failed since but the squeak has gotten to be horrific and I cannot recommend any of these products to people with glasses.
I've purchased these ear cups a long time ago, and I don't use these headphones to much anymore.
When I do use my Sennheisers, the softness is still lasting and has not cracked.