What characteristic of plastics allows them to be molded into complex shapes?

The characteristic of plastics that allows them to be molded into complex shapes is malleability under heat and pressure. Plastics are typically thermoplastic or thermosetting materials. Thermoplastics can be heated to a temperature where they become soft and pliable, making them amenable to various molding techniques such as injection molding, blow molding, and extrusion. Once shaped and allowed to cool, they retain the form. The ability to soften upon heating and solidify upon cooling enables manufacturers to create intricate designs and detailed components from plastics, which is a fundamental advantage in applications ranging from consumer products to automotive parts.

The other characteristics listed do not directly contribute to the molding process in the context of shaping plastics. Thermal stability refers to how well a material maintains its properties at elevated temperatures but does not directly imply moldability. Elasticity describes a material's ability to return to its original shape after deformation, which is not the primary factor for molding. Conductivity typically relates to how well a material can conduct electricity or heat, which is not relevant in the context of the moldability of plastics.