Final answer:
Amorphous thermoplastics are formed above their Glass Transition Temperature (Tg). When the temperature rises above the Tg, they transition to a softer and more flexible state.
Step-by-step explanation:
Amorphous thermoplastics are formed above their Glass Transition Temperature (Tg). When the temperature of a thermoplastic rises above its Tg, the material transitions from a rigid, glassy state to a softer and more flexible state. This occurs because the molecules gain enough thermal kinetic energy to allow internal rotation and independent sliding, rendering them deformable.