25 10x13 Poly Mailers & 500 Thank You Stickers 𝗗𝘂𝗿𝗮𝗯𝗹𝗲 𝗠𝗮𝗶𝗹𝗲𝗿𝘀】: crafted with polyethylene plastic material, durable, waterproof and tearproof, which making them not easily punctured and damaged. 𝗦𝘁𝗿𝗼𝗻𝗴 𝗔𝗱𝗵𝗲𝘀𝗶𝘃𝗲 𝗦𝗲𝗹𝗳-𝗦𝗲𝗮𝗹𝗶𝗻𝗴】: Each polymailer 10x13 contains a strong adhesive self-sealing strip. The strong stickness prevents your items from being secretly replaced during transportation. Simply peel and fold over to seal each package safely and securely.