If you insist, but *very* minimal in the econ seats. I could feel the weft of the seat pan support mesh fibers when I pressed my fingertips down on the seat cover, which would mean no more than about 1/2" of fill at the outside. Also, because I'm quite short-legged, the waterfall edge isn't enough to prevent the back of my calves from pressing against the seat pan frame. All in all, a noticeably stiffer seat surface than is usual on a US commercial aircraft.
I've got an Aeron chair at the office, and the exposed mesh seat is quite comfortable, but then, the seat pan height is adjustable, and I don't sit in one position and not move my lower body at all for several hours when I'm sitting in it. I'm fine in Frontier econ for 2 hours or so, but more than that starts to veer into diminishing returns territory.