Tyvek® (White Spun Bonded Olefin) Open End Catalog with Kwik-Tak® - Open End Catalogs have their flap on the short dimension and center seam construction. These envelopes are made using an extremely strong, lightweight, moisture resistant material. They have a pressure-sensitive seal that requires no moisture. Release tape covers the adhesive until the envelope is ready to seal.Bright White Spun Bonded Olefin Smooth Finish Center SeamPressure Sensitive Seal Flap Down