I'mnot sure what it is, but without too much TMI, let's just say that I'm more comfortable on a Brooks than anything else I've owned "in that way". I've had a small old MTB saddle, one of those gigantic padded Bell saddles, a Specialized Rival, a Specialized Sonoma, and a Bontrager. All, eventually, caused those bits to go numb or experience some sort of discomfort. My Brooks, OTOH, caused it once - on my LHT when I first got it. The saddle was pointed up too high for the riding position, and after adjusting it's been fine.
Again, dunno what it is, but that's how I sell my wife on it.
