Strong & Tamper-Proof Design: Made from durable 55–60 micron polyethylene material with a high-strength self-adhesive seal. Once sealed, the bag cannot be opened without visible damage and Our Mailing bags incorporate a permanent self-seal closure and are made from an opaque 60 micron film. Strong Multiple Color Mail Postage bags, ranging from Small to Large Non-Transparent- Any items Placed in the bag are Opaque not visible through the Material Strong Adhesive- High performance 55mu bags, strong adhesive perfect for Shipping and Packing small, Business works or Personal Beloging shipment to your loved once Our posting bags have a self-adhesive strong closure. These air sealed postage bags are water and dirt resistant and made to secure the inside and outside.