Abstract: Provided herein are aqueous resin solutions providing passive opacification and products incorporating the same. The opacity of the water-based materials provided herein change over a desired temperature range increase (0° C. to <100° C.) at ambient pressure. A specific epoxy functional resin/polymer suitable for the resin solutions are prepared by reacting (A) an epoxy pre-polymer of (1) one or more polyols and (2) one or more epoxy functional materials with (B) a di- or polyamine, and upon formation, dissolution in water, and neutralization, an ionic strength adjuster is added, thereby forming the passive opacification resin solution. The resin solutions are substantially free of cross-linking agents.