Thermally developable imaging materials have an outermost protective layer that is composed of one or more hydrophilic film-forming components. The predominant film-forming component is a negatively-charged latex polymer that has negatively-charged ionic groups other than carboxy groups. The latex polymer is present as latex particles that have been prepared in the presence of a nonionic stabilizer in an amount of at least 0.5% (by weight) that has an HLB value of 7 to 20. The nonionic stabilizer becomes associated with the latex polymer particles. Both thermographic and photothermographic materials can be prepared with such protective layers.