Perforex film
These are used to more or less control the resin flow during vacuuming. Sufficient resin must remain in the laminate to make a good bond between the fibres themselves and any core material. For this reason, various films are available with many or few perforations. for more info: https://www.v-sure.eu/en/vacuum-perforex-ela20p1-h1200-5-m2