Had a pair of velour and a pair of sheepskins from the last massdrop arrive today. Cut off the thin layer of film on the dekoni pads and kept stock dust covers in. Impressions are on my unmodded HD800 (warning; I prefer a very bright sound, preferring unmodded over HD800S and SDR mod), wearing glasses, and compared stock pads that have been worn down over 5+ years of use
Velour;
Construction: soooo thick (1 extra o for each degree of thickness, literally about triple the thickness of worn stock pads) and comfortable, material is somewhat softer and less scratchy and less prone to catching my hair.
Sound: Sound is more distant but somewhat less airy. Soundstage seems to have shrunk a bit as a net result. I love detail, and had to up the amp to 1:30 oclock versus stock at 12 for the same level of clarity. Bass is ever so slightly more present but more muffled. I assume these are all a direct result of the drivers being further away from head.
Sheepskin;
Construction; Leather feels thin and somewhat plasticky, certainly not as 'premium' as the, say, audeze leather pads. This is to be expected I guess. Nice amount of conformity and formed a perfect seal around thick rimmed glasses.
Sound; I think this is a direct upgrade FOR ME. It gives a very slight elevation to the bass (i would estimate no more than 1dB, and do not expect the same tonality of HD800S bass), increased the clarity, and soundstage was relatively unaffected at 12 oclock. Imaging seems to be ever so slightly more pinpoint-accurate (is that even possible?). The net result can be perceived as 'brighter' than the stock HD800, perhaps reflected in the elevated treble in measurements, but I find that it is just right for me. I would attribute all these as a result of a better seal due to the better conformity of the pads.
I have also briefly auditioned a HD800S with fenestrated pads, and thought that it was relatively unchanged from stock HD800S. If anything the sound, especially lower mids to upper bass, was weaker and more scattered. I think all these observations are what are expected from measurements and materials. Overall, the build quality is good, not great, but it is cheaper than Senn's own replacements.