Dave,

I may be wrong, but those look like seat pads that you put on top of rigid seats. I don't think they'd work well as a stand-alone seat.

Sweet Composites has good prices for minicell. http://sweetcomposites.com/Minicel.html

This is from another post where I explained how I made a minicell seat for my son's kayak; it should work for adults as well:

Problem: I wanted to carve a minicell seat for my boy's kayak, but how would I know what shape to give it? A five year old isn't going to be able to tell you where you need to remove more material in order to get a better fit.

Solution: I made a mold of my son's bottom while sitting in a padding position and used it as a reference to carve the seat.

I took the memory foam mattress topper from our bed and folded it three layers thick on the floor and up against a wall. I cut a garbage bag open and laid out some strips of plaster bandage on it. I used four layers of plaster bandage, two layers with the strips laid front to back, and two layers with the strips running side to side, alternating with each subsequent layer. The plastic with the plaster bandage went on top of the memory foam (the plastic is there to protect the foam) and my son went on top of the plaster bandage. I made sure to keep him in positon with his back up against a spare block of minicell acting as a backrest and his feet at the proper distance from the backrest. Ten minutes later, I had a good mold of my son's bottom and upper thighs.

To carve the seat, I made four cardboard cross sectional forms for different parts of the seat. One was for the shape right down the middle from front to back, and three were for the shape of the seat from one side to the other. The three side-to-side forms were for the front, near the back where the sit bones (ischial tuberosities) are located, and one in between those two. As I carved the seat, I checked my progress with the four forms and "faired-in" the areas in between. It worked like a charm and took the guess work out of carving a seat.

Pedro Almeida