My M-80's underside seems just fine but I haven't even had them for a full year yet, and they're the black/shadow ones. The underside (center) of the band is this sorta neoprene-like fabric tho... I think if anything would stain first it'd be the side edge (that wraps around to the top), it's sort of a smooth suede, assuming the shadow & white ones use the same materials anyway. Maybe someone with the white ones can chime in. The headband's not that large, maybe an inch?
M-80 look deceptively large in pictures, the cups aren't larger than an average ear (my large ears peek out from the top/bottom, just a bit) and the forks are maybe two inches wide at most (going off memory, I can measure them if anyone's really that curious); point is I'm not sure you'll sweat any more because they're hanging from your neck. Now if you're walking a few miles outside in the summer, that's a different story.
I was surprised at how small they were when I first saw them, even tho they're on ears so they aren't supposed to be huge.
msavic6, I'd definitely characterize them as fun sounding... Bass is punchy but not overdone, mids are very nice (they actually render some vocals a little sweeter than my Beyers even tho those are clearer sounding overall), highs are a little rolled off but it's not massive and works well with the overall sound (and some of my other headphones are a little bright, hf3/DT880, so I'd be put off if the treble roll off was too exaggerated). They won't satisfy a total basshead but they're still on the warm/fun side of things.
I think they're an excellent value as an overall package, specially for the price they've been going for on Amazon ($150-160); once you factor in the durability, the removable cable(s), the nice case (even tho sometimes I don't even use it when I toss them in my book bag, I still use a pouch tho), the excellent warranty, and even the looks... Makes a very strong case even for MSRP. If they were full size closed cans with the same sound but none of the extra perks I probably wouldn't rate their value quite that high, but for portables they mark a lot of the right boxes.
Too many portables out there are built out of this mix of glossy plastics and the same sorta angular design, dunno, it's starting to get monotonous. I wasn't crazy about the M-80's sorta goth/punk look but it grew on me and they aren't as flashy as they look on pictures (well the black ones aren't...). I like some of Philip's recent designs too, sorta retro but still built very very well. Looks aren't my first or second consideration but c'mon, if you're gonna wear them in public it factors in unless you're a schmuck (says the guy who looks like a hobo at the moment after not shaving for a week or two...).