What is Saddle Flex?

What is this "saddle flex" some of you experience? Is it horizontal movement of your saddle?

In general, is saddle flex a bad quality?

It's a twisting around the rails. I don't know if you would consider that horizontal or what. I'm not an expert, but I don't think the saddle is a place where flex is a useful shock absorber; it's only going to rob you of power.

(Generally, although an engineer will tell you that "flex" in some places is desirable, in common parlance I think people always mean a "bad quality" when they say flex.)

My guess is same as Oakleaf's -- but maybe twisting around of the shell and the rails.

A little vertical shock absorption from titanium rails is a good thing but you don't want them twisting side to side.

Hmm, Fizik explains their flex here:

http://www.fizik.it/technologies_wing_flex.aspx

and here:

http://www.fizik.it/technologies_twin_flex.aspx

But those are both good types of flexing. I rode a saddle that was sagging like a hammock front to back at the velodrome, it was hell since we're always in the drops. I finally pulled off the track and nosed it down but ugh. Our instructor thought I was quitting and kept asking what as wrong. "Uhhhhh, my crotchel area hurts and the last time something was this far up it, it had a pulse." Poor Paul, so sweet, but so concerned at times I don't want to announce my problems to the world.