Which statement describes a thermosetting polymer?

A thermosetting polymer is characterized by its ability to undergo a chemical change when heat is applied, resulting in a hardened structure that cannot be reshaped or remolded after the initial setting process. This irreversible reaction occurs when the polymer chains cross-link, creating a strong three-dimensional network. Consequently, once a thermosetting polymer has been set, it cannot be reshaped with heat again, making the correct statement that it can only be reshaped once when heat is applied.

In contrast, the other statements are not accurate descriptors of thermosetting polymers. They typically do not retain flexibility and elasticity— properties more aligned with thermoplastic polymers. Furthermore, thermosetting polymers are not water-soluble; instead, they are designed to be resistant to chemicals and moisture, which adds to their durability in various applications. Thus, the unique characteristics of thermosetting polymers underscore why the correct statement accurately reflects their behavior and properties.