Thermally stable polymers, which have a high proportion of aromatic structures, are also called high-performance plastics; this application-oriented classification compares such polymers with engineering plastics and commodity plastics. The continuous service temperature of high-performance plastics is generally stated as being higher than 150 °C, whereas engineering plastics (such as polyamide or polycarbonate) are often defined as thermoplastics that retain their properties above 100 °C.⁠ Commodity plastics (such as polyethylene or polypropylene) have in this respect even greater limitations, but they are manufactured in great amounts at low cost.