I did go to Evercoats web sight after Brian made his post. They list the Featherfill as a high build polyester and the Slick Sand as an extra high build polyester. I am looking forward to trying it.
Back in the 70's the first polyester primer I ever heard of was a brand called Eliminater. I painted my 47 Ford conv with it. Shot the car with S/W acrylic enamel with Polysol. Believe it or not that car is still around with that paint job still on it. The modern primers are unbelievably good.