PERFECT SIZE：7.5 x 5.5 inches, Pack of 50 PCS. Shipping label sleeves will hold most printed mailing labels such as packing slip, mailing documents, invoice, labels etc. WATERPROOF：Packing slip envelope pouches have self-sealing for easy packing with a tamper-evident, super secure closure. Pressure sensitive adhesive provides a high strength, durable closure that is water and dirt resistant. Sensitive backing attaches securely to almost anything - paper, wood, plastic or metal. EFFICIENT：Packing list mailing envelopes make sending labels easy and efficient. No more taping return labels for UPS or FedEx. With these plastic shipping label sleeves with adhesive you can just slip in the paper, without taping, you can be rest assured that the ink won't smudge in transit because the plastic protects the label for a clean and professional look, saving you much time and money. This method a lot easier than using tape to secure the label to a box or package