Works with first class mail. Pink Cat Design over pale grey outer surface/Pink inner lining - Cat design printed on both the front and back of each bag Unsurpassed Water & Tear Resistance - 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 - 100% recyclable