Thermally developable materials include an imaging layer containing a non-photosensitive source of reducible silver ions. Disposed over the imaging layer is a barrier layer that comprises inorganic filler particles that are intercalated or exfoliated with a hydrophilic or water-dispersible polymer. The particles have a length to thickness ratio of from about 10 to about 1000. The barrier layer can prevent migration of diffusible imaging components and by-products resulting from high temperature imaging and/or development. These thermally developable materials include both thermographic and photothermographic materials.