Dark Security Opaque - In addition to the heavier paper, a dark opaque design is used to further protect contents from view.
Additional Security Text - Twofold also add the unique Checksecure text pattern, the combination of dark opaque and text prevents envelope scanning by powerful light sources such as halogen lamps.
Royal Mail accepted – Royal mail insist on envelopes used for their premium services such as ‘clean mail' or ‘business mail' having no less than 85% opacity i.e. contents must not be viewed by their sorting machines using powerful halogen lamps, Twofold Checksecure envelopes are above this required standard.
Mail Verifying Sprays – Checksecure envelopes cannot be scanned by application of solvents such as ‘scan mail' spray; application of solvents simply reveals the Checksecure opaque design inside the envelope, protecting contents from view at all times.