These polypropylene envelopes feature a light-weight, yet durable construction that resists moisture, stains and tears to protect valuables from the elements. They have heat-welded seams, making them more durable and long lasting then traditional paper envelopes. In addition, the see-through design allows for easy identification of the contents and the top flap seals securely with either a string fastener or Velcro closure. They are great for office, school, craft, hobby, art and home.