There are, or were, some other manufacturers using a different but somewhat similar product. I have no idea though how well it worked, if at all. One I knew of had terrible wrinkling problems.
I always recommended the thickest heaviest density foam you can afford. I'm near San Francisco and easily notice a difference between a 4x2, 1# compared to a 6x4, 2# cover.
Personally, I think sunbrella is EXTREMELY over priced. Yes, it will last "forever", but the rest of the cover will fail long before then, requiring the entire cover to be replaced. There's no pint in having one aspect of the cover last 100 year if the rest of the cover is only going to last 8.