Abstract: A security envelope for transporting valuable documents and articles includes a thin header formed of thin frangible material secured to the back panel having an adhesive layer that seals the header to the front panel upon folding and pressing closed. An inner layer of adhesive on the inner surface of the back panel seals the inner front and back panel surfaces to close the envelope chamber and extends further toward the envelope bottom than the header adhesive layer when sealed to prevent tampering tool access to the envelope chamber. Application of tampering heat will shrivel the header and cold sufficient to release the inner adhesive layer will cause pieces of the outer adhesive layer to break off and fall away. Printed indicia on the header inner surface and a transparent flood coat on the inner header surface will adhere to the header adhesive layer and aid in the tampering attempt indication.