I do not know it depends on the sheeting. I am sure 1/16th it may soak through but on thicker might not. If I was using sheeted foam I would prob use the water based poly U. when using water based on open framework with thin sheeting it can cause slight warpage sometimes but if your sheeting is stuck down to a foam core I dont see a problem as the core will keep it from warping. if I was using the laquer based I would use a couple coats of sanding sealer as that will keep the poly from soaking all the way through the wood.

Joe