Works with First Class Mail. Flat Pink, White, & Gold Design outer surface/Grey inner lining - Whimsical design fully covering 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 -