These OEM Tamper Evident Envelopes feature flaps with patented tamper indicating panels. Once flaps are raised, the words 'OPENED' appear in red and cannot be repaired to hide evidence of tampering. Made of DuPont Tyvek, these water-resistant and moisture-resistant envelopes won't rip, tear, or puncture, offering a much stronger and more secure design than traditional paper envelopes. Lightweight to save on postage costs, they are also easy to use with a simple peel and seal mechanism.