HEAVY DUTY ENVELOPES: They offer excellent protection against rips, punctures, and moisture and are practically indestructible. They are safe and self-sealing as well. INDESTRUCTIBLE DESIGN: Sturdy, Robust, and Lightweight Tyvek Waxy Material Is Resistant to Rain, Moisture, Tearing, Ripping, and Other Common Postal Threats EASY SELF SEAL CLOSURE: Simply peel back the sticker to quickly and easily seal and send. Quick paper and packet stuffing is made possible by open-end catalog orientation. SUPERIOR SHIPPING PROTECTION: Maximum Security for Confidential Business Mail is Provided by Double Reinforced Construction, Opaque Color, and Super Sticky Glue.