500 9x12 Yellow Poly Mailers Envelopes Bags Self Seal Bag Genuine ValueMailers TradeMarked Product , Yellow Self Seal Poly Mailers Water, Tear and Puncture resistant. The silver inner layer provides confidentiality The self-seal closure provides a reliable, tamper-evident seal to secure all enclosures, while being opaque, the exterior film creates a crisp, professional image for your company. High-efficiency mailers are perfect for shipping a wide variety of non-fragile items.