What makes a seat comfortable?

[Karoozer]

I need to reupholster my seat  (R 80 G/S) and would like to make it as comfortable as possible while I am about it.
My experience in mountain biking has shown that a big padded seat is not necessary the most comfortable.
Is it the shape?
The hardness/ softness?
Outer covering?
Quantity of Iron in the butt?
All of the above?

Thanks!

 

[Sho`t Left]

 

[passin]

 

[letsgofishing]

 

[Karoozer]

 

[GreenMamba1974]

 

[ratrap]

 

[Dunce]

 

[Duke916]