A primer layer and a thermoformable film that includes the primer layer are provided. The primer layer includes a cross-linked adhesive polymer having a semicrystalline region and a polar region. The cross-linked adhesive polymer has a tensile strength at maximum elongation that is less than that of an otherwise identical adhesive polymer that has not been cross-linked. The primer layer can be an outer layer of the thermoformable film, can be positioned between two additional layers of the thermoformable film, or a combination thereof. The primer layer can be positioned in contact with a mold surface during a thermoforming process.