To make xps foam letters look smoother and more like painted wood.
The process is straight forward but time consuming. Not viable commercially but can make an interesting project for creative folk.
First buy the letters already cut to shape on ebay or elsewhere.
Sand the letters to shape with a medium or coarse grade sand paper.
Use a paint brush to apply three layers of water proof PVA allowing each layer to dry.
Sand the surface smooth with wet and dry sand paper 180 grid.
Paint the surface with vinyl matt emulsion and the result is quite convincing.