Different plastics are used for the thermoformed film, and polyvinyl chloride (PVC) is the most
commonly used plastic, for its chemicoephysical characteristics
and low cost (Allen, 1999; Van Dooren, 1991). The lidding material
is generally a metallic foil able to guarantee the durability of the
packaging and to allow it to be broken under pressure; aluminum
foil fulfills these requirements.