Thermoplastic polymers are materials that can be softened when heated and hardened when cooled. This is due to their molecular structure, which allows the polymer chains to slide past each other when heated, making them moldable. Upon cooling, they solidify into the desired shape. Examples include polythene, polystyrene, and PVC.
In contrast, thermosetting polymers, like Bakelite, harden permanently when heated and cannot be reshaped after that. Fibres are not specific to this property but are a type of polymer used in textiles.
Therefore, the correct answer is thermoplastic polymers.
Match the following polymers with their applications: