Abstract: Disclosed is a method for treating a thermoplastic substrate for improving the surface thereof without significant loss of physical properties. Such method comprises:(a) determining the solubility parameter, .delta..sub.T, of said thermoplastic substrate and the surface energy, .gamma..sub.T, of said thermoplastic substrate;(b) determining a set of destructive solvents which are detrimental to a physical property of said thermoplastic substrate;(c) determining a set of non-destructive solvents which are not detrimental to the physical properties of said thermoplastic substrate;(d) determining the solubility parameters for said set of destructive solvent, .delta..sub.D, and for said set of non-destructive solvent, .delta..sub.N ; and the surface tension for said set of destructive solvent, .gamma..sub.D, and for said non-destructive solvent, .gamma..sub.N ;(e) selecting a subset of said destructive solvents which possess solubility parameters, .delta..sub.