Ampac Tamper Evident Security Envelope 335x430mm C3 (Pack of 20) KSTE-3. Ampac Tamper Evident Envelopes feature a tear off redemption slip, which provides you with a sequential number, allowing you to track or trace your envelope. The double seal displays a void message if tampered with, helping to keep items secure in transit. This pack contains 20 C3 envelopes. Sequentially numbered envelopes for easy tracking. 100% recyclable. Displays a visual message once open if tampered with. Size: C3 (335x430mm). Resistant to solvent-based attack. Supplied in a pack of 20. Opaque.