Which property is associated with plastic as a material in product design?

Plastic is known for its lightweight and moldable properties, making it an ideal material in product design. The lightweight characteristic allows products made from plastic to be easily handled and transported, contributing to efficiency in both manufacturing and usage. The moldability of plastic means it can be formed into complex shapes and structures during the manufacturing process, such as injection molding or extrusion. This versatility enables designers to create a wide array of products tailored to specific functions and aesthetics without excessive material waste.

The other options highlight qualities that do not align with the common characteristics of plastic. While some plastics can be strong and rigid, they are typically not associated with being heavy or hard to shape, as plastics are generally celebrated for their ease of manipulation and lightweight nature. The eco-friendliness of plastics varies, and while some bioplastics offer sustainable options, many conventional plastics are not inherently sustainable or eco-friendly. Therefore, the accurate distinction of plastic's primary attributes in product design is its lightweight and moldable nature.