Which type of materials cannot be reshaped after they have set?

Thermosetting materials are designed to harden permanently after being subjected to heat and/or pressure during their production process. Once thermosetting polymers (or resins) have cured, they undergo a chemical change that makes them rigid and unable to be remolded or reshaped.

This unique characteristic is due to the extensive network of cross-linking that forms between the polymer chains when these materials set. It is this cross-linked structure that provides excellent strength and thermal stability but also means that the material cannot be softened or reshaped through heating once it has fully cured.

In contrast, thermoplastic materials can be reheated and reshaped numerous times without undergoing any significant chemical change. Flexible materials (which can include some thermoplastics or elastomers) are also designed to be bendable and reshaped. Ceramics, while they can be difficult to reshape once fired, are typically categorized differently than thermosetting materials due to the fundamental differences in their properties and the processes through which they are made and reshaped.

Thus, the defining feature of thermosetting materials is their irreversible hardening process, which makes them distinct in terms of reshapeability after setting.