but when the temperature is below the vitrification temperature, the polymer is under glassy state, which is hard solid, wherein energy from the molecular thermodynamic movement is low, the elastic modulus is large, and the deformation is reversible, under such aggregative state, it is not suitable for molding with large-scale deformation. When the temperature is above the vitrification temperature, the plastic will become softer, and therefore, the vitrification temperature is maximum temperature that can be used for plastics. The lower limit temperature applied to plastics is called the brittle temperature, below which the plastics will easily get cracked and damaged under stress.