To facilitate the computation of the field scattered by a thin non-magnetic dielectric layer, it is customary to model the layer as an infinitesimally thin resitive sheet, but the simulation becomes increasingly inaccurate at oblique angles of incidence when the electric vector has a component normal to the layer. By starting with a volume integral formulation of the scattered field, it is shown that the accuracy is greatly improved when a “modified” conductive sheet is included in addition to the resistive one. The boundary conditions for the new sheet differ from those of a standard conductive sheet by the presence of a second normal derivative, and the combination of two coincident sheets yields results for a thin layer that are virtually indistinguishable from those provided by a volume integral equation. The advantages of this type of simulation are discussed, and the extension to a layer of arbitrary shape and composition is described.