Coretek flips meet the highest standards and specifications published by museums for archival composition and content. To meet this standard, Coretek uses a polyester film that is 100% uncoated, colourless, biaxially-oriented PET. The holders are clear and colourless because the material is pure. That means NO plastic, NO additives or UV inhibitors, NO surface coatings, and NO absorbents or other contaminants. Storage flips containing PVC, dark tints or oily residues, do not meet this high standard. Flips that have a coating, stick together, or take a heat seal do not meet the Coretek standard, because pure PET is smooth and can only be sealed ultrasonically.