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, providing a much stronger and more secure option than traditional paper envelopes. Lightweight design helps save on postage costs and ensures ease of use with a simple peel and seal mechanism.