The smooth surfaced product described here demonstrates how surface characteristics of glass-reinforced plastics can be modified to allow painting of automotive and truck body parts with the minimum of surface preparation. This new product effects substantial reduction in finishing costs. Methods of measurement of surface roughness are given and data are related to factors that affect the surface characteristics of the parts. Uniform preforms of reproducible quality contribute materially to obtaining smooth surface products which in the unsanded condition show only 25 μ in. roughness and 450 μ in. or less fine waviness.