I'm thinking of covering my seat in Lycra. I got the leather piece on but it had big folds sticking out on the back corners. Same with the thinner vinyl but less so. Couldn't figure out a way around it. Then I put this stretchy black fabric on it & no wrinkles. Smooth all around. I know from my bicycles seats that the sun fades Lycra after a couple of years in but replacing it should be easy. Staple gun & scissors. Can't find Lycra in stores though, just stuff that resembles it. Hmmm....just had a thought. Neoprene. Like in scuba suits.  

Hey Babbalou, lycra is available in large fabric stores as swim suit material, or go to a Goodwill store and buy an old bathing suit, Granny type should give you all the heavy weight lycra you need.

Another place to get good quality lycra, bicycle shorts. My kids bought me some that have a padded crotch and inner leg when I was using my 10 speed. They are made of good heavy weight lycra. I have seen them at garage sales & good will stores real cheap.

Are they dense?

One thing about Memory foam that I learned the hard way - is that not all memory foam is created equal! I purchased a 4" 5lb rated (most dense) Matress Topper from a "reputable" source on Ebay. After less than a year, the "memory" has "forgotten" itself. Now it's just a soft foamy topper. I'm pretty disappointed.

If I were to buy some for a seat project, I would want to make sure it's really high quality stuff.