CPET (Crystalline Polyethylene Terephthalate) is used primarily for ready meals. Production is based on the esterification reaction between ethylene glycol and terephthalic acid and is partially crystallised, making it opaque. As a result of the partially crystalline structure, CPET retains its shape at high temperatures and is therefore suitable for use with products that are to be heated in ovens and microwave ovens. Standard for almost all CPET products is an APET top layer, which has particularly good sealing properties and gives the products an attractive, lustrous appearance. The precision control of the material's crystallinity means that the product can be used within a temperature range of –40°C to +220°C. This meets the needs of consumers, who require good impact resistance at low temperatures and shape retention at high temperatures. CPET also forms a highly effective barrier against oxygen, water, carbon dioxide and nitrogen.