I've used PPG K200, and thought it worked well. I guess it's replaced by K38. The tech sheets say they build to 3 mil dry film thickness. The DuPont 2K Ultra Productive Primer-Filler 4904S fills to 6 mil. Is this what you guys are talking about? It does take a lot to get a product to build that thick and not crack, shrink, pop, lift, or any of the other problems that occur when painting a car. The thicker it builds, the fewer times you need to mask, suit up, mix, and shoot. This is what makes it worth the price. If you're doing a 5 year restoration, then I guess it doesn't matter.