AIR as the TOP LAYER is, so far, working best in my Kris Holm Fusion Saddle. [But I have yet to try gel.]
When purchased the Fusion came with just the fold over, double-high, dog bone shaped bladder and 20-inch (I think) tube. Quite comfy, but the saddle didn’t hold its shape well, kinda squashed to the side on me, so I purchased 1-inch foam insert from Unicycle.com.
With FOAM installed next to saddle TOP and dog bone air bladder underneath, comfort went down dramatically. I attribute this to the crotch on saddle movement against the foam creating more friction, heat and chafing. The foam is more rigid than the air had been with bad result.
I changed the layering and reinstalled the foam as the middle layer between air top and air bottom. The dog bone bladder folded easily over the foam and was easy to install.
Now with AIR - FOAM - AIR, the saddle is most comfortable and holds it’s shape well. I attribute the increased comfort to air just beneath the cover that probably gives with crotch on saddle movement thereby reducing friction.
QUESTION TO GEL USERS: Is it worth my while to try gel instead of air immediately beneath the saddle cover? (A gel seat cover would probably wrap around this 1-inch foam insert nicely and might make a comfy top layer inside. With added thickness, I would move to a single layer air bladder next to seat base.)