Manufacture of thermoformed containers

A method of forming a container comprises a first stage of forming an intermediate article by a first process comprising providing a sheet 2 composed of a biaxially orientable thermoplastic material; heating the sheet to a moulding temperature which is above the glass transition temperature (Tg) of the thermoplastic material, wherein the moulding temperature is within a range of from 5 to 25 °C above the glass transition temperature (Tg); and thermoforming the heated sheet using a mould tool to cause at least a portion of the annular sidewall, and optionally at least a portion of the bottom wall, to be stretched from an initial thickness to a final thickness and the final thickness is less than 45% of the initial thickness, thereby to be biaxially oriented with a strain induced crystallinity of at least 27%. A second stage thermally conditions the intermediate article at an annealing temperature of at least 135 °C to anneal the respective portion or portions by relaxing amorphous regions between strain induced crystals and causing the strain induced crystals to grow in dimensions, wherein after the heating step the strain induced crystals having a maximum width dimension of 500 nm. A third stage forms a container from the intermediate article by cooling the intermediate article from the annealing temperature to a quenching temperature of no greater than 90 °C to quench and rigidify the bottom wall and annular sidewall and form the container.