When hot water is placed into an empty water bottle, the bottle keeps

When hot water is placed into an empty water bottle, the bottle keeps its shape and does not soften. What type of plastic is the water bottle made from?

Thermoplastic
PVC
Polyurethane
Thermosetting
This question was previously asked in
UPSC CDS-1 – 2019
The question describes a water bottle that retains its shape and does not soften when hot water is placed in it. This property is characteristic of thermosetting plastics. Thermoplastics soften upon heating and can be reshaped, which is why typical PET water bottles deform when exposed to hot liquids. Thermosetting plastics undergo irreversible chemical cross-linking during their formation and remain rigid when heated; they will eventually decompose or char at very high temperatures but do not soften.
– Thermoplastics soften and become pliable upon heating.
– Thermosetting plastics remain rigid upon heating.
– The bottle not softening with hot water indicates it is not a thermoplastic.
Common water bottles are made from PET, a thermoplastic. However, if a bottle is designed to withstand hot water without softening, it is likely made from a thermosetting plastic or a specialized high-temperature thermoplastic, but given the options and the definitive statement “does not soften”, thermosetting is the most fitting category. PVC is a thermoplastic, and while some polyurethanes can be rigid, the description points towards the general class of thermosets.