Since films typically run within a thermoforming process in unsupported type web equipment,dimensional stability of the webs allows the process to function properly. A web material that shows aconsistent degree of change in dimensions in the cross and machine direction throughout the
thermoforming range typically works well. For this reason, the pharmaceutical industry has relied heavily on PVC films since this particular attribute helps a machine maintain good registration throughout the forming, filling, sealing, perforating, and punching operations commonly used in
blister packaging. Selecting a film with a degree of cross-directional growth when subjected to
thermoforming temperatures represents another important attribute that aids in robust processing.
Not every film delivers a solution here, but other types of polymers, such as homopolymer and copolymer
polyester based films, can also work well in this function.