polyurethane is a wood finish that you can buy in most all home depot, Lowes, home improvement stores. They make H2O based and oil based. It works well to fill the micro holes in solartex, and give you a mirror finish. You can apply this over paint as long as you make sure that it is compatible with the paint. Be careful though because it will stack the weight on if you arent careful. I reccomend the water based and thin it out. Treat it like a clear coat

Hope it helps

JB