Thermoplastics which consist of approximately 80% of crystalline structures are called semi-crystalline materials.
Their structure is ordered with some disordered areas in between.
The ordered areas give the material strength and stiffness.
Due to the higher stiffness, the material will break rather than bend when a load is applied.
Typical examples of semi-crystalline polymers are PA, POM, PP and PE.

Semi-Crystalline in Plastic Industry