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 Seam Pressure Sensitive Seal Flap Down