Sand Dollar Poly Mailers 10x13 Pack of 25 Unsurpassed Water & Tear Resistance. USPS APPROVED FEDEX APPROVED UPS APPROVED Superior side seams combined with Heavy Duty polyethylene make these High Quality envelopes highly resistant to water, punctures, and tears. Pressure sensitive self seal. Easy packing, tamper-evident, and super secure closure. Light Weight & Time Saving! Lower shipping costs combined with faster shipment preparation equal big savings over other packaging option. 100% recyclable!