Free films are mainly used for permeation or strength and elongation
testing. There are several techniques described in literature but the
most common free films are prepared by the lay down technique on a substrate
with a non-stick surface. Leneta polyethylene
sheet or TeflonŽ sheet are good examples of such type of substrate. After production, the wet films are dried for a specified time under
defined conditions of temperature and humidity. After this period the
film has to be separated from the support. During the process of separation
the coating should not be changed in any respect (thickness,
size, stressed, porosity,
etc.).