Size AND SHAPE. The most comfortable saddle I ever used elicited gasps of horror from everyone who looked at it (never could convince anybody to actually try one). The Cinelli Unicanitor mod 50 or 55 (the saddle in question) was a bare nylon shell, made to mimic a well-broken in Brooks, minus the leather care issues. The combination of shape and flex fit my "sit upon" perfectly, like no other saddle (including Brookses and other Unicanitor models). Too bad they quit making 'em 25 years ago. I still have 3 of 'em, and even though I ride a 'bent these days, they are not now, and never will be, for sale.

SP
Bend, OR