A release film is used primarily to ensure that the breather fabric does not bond to the curing resin. The release film can also be used to control the amount of the resin that is allowed to be drawn out of the pre-preg (and absorbed into the breather fabric) to ensure the correct fibre ratio within the cured laminate.
                                                                                                                         
Unless a peel-ply is to be used, the release film is placed in direct contact with the reverse (non-tool) face of the laminate. Consequently as the name suggests, the release film must  also release from the cured laminate.

VAC Innovation fluoropolymer release films are either FEP or ETFE.

FEP film is red (VACleaseXXR1.2) is colour whilst ETFE film is blue (VACleaseXXB1.2).

Both films provide release from the majority of resin systems.