Wholesale Prices! 2500 Minimum. 1-1/2" Flap. Fits 1950-1962 Comics. Polypropylene is a crystal-clear, high sheen, crisp material. We use bi-oriented polypro which means that when the material is made, it is stretched in both directions so that in time it will not "pucker". Excellent contact clarity. Use for Long-term storage.