Many industrial polymer processing operations (e.g., extrusion, injection molding, etc.) include solid-to-liquid or liquid-to-solid phase changes at non-isothermal interfaces. Stickiness (tack) can occur depending on the process conditions. However, prediction of tack formation is not trivial. This work presents a hypothesis for tack formation between molten polymers and solids under non-isothermal conditions. Our hypothesis states that strong adhesion requires wetting (and thus surface creation) at the interface upon contact and, consequently, contact temperatures above the polymer's solidification point. Lower contact temperatures result in a solid-solid interface with negligible adhesion. It was suggested that the contact temperature determines the existence or non-existence of surface sticking. The hypothesis was supported by non-isothermal tack experiments, which showed that the change from stickiness to non-stickiness was surprisingly pronounced with changing surface temperature of the solid material. From a practical perspective, the work may be useful both for professionals (e.g., designing new processing equipment and performing process troubleshooting) and home users (e.g., working with hot melt glue or 3d printers). (C) 2016 Society of Plastics Engineers