This paper examines the stationary temperature and stress fields in an orthotropic elastic slab containing a plane interior region which resists heat flow. Over this region of imperfection the heat flux is assumed to be proportional to the local temperature difference, whereas the stress and displacement components are taken to be continuous. Each face of the slab is subject to an arbitrary temperature variation. Numerical results are given for isotropic and orthotropic slabs with flaws of various lengths and heat-flow resistances.