The A1 Invitation Envelope (3 13/16 x 5 3/16) in 1.6mil Cellophane is a transparent envelope made of polypropylene, which will not rip, wrinkle, tear or fog. This envelope has a square back flap and is suited for RSVP cards, invitations, announcements, and notes.The A1 is easily sealed by a an adhesive strip, and its dimensions make it the most common envelope used for RSVP as the A1 size fits inside all other "A" envelope sizes. Available both plain and printed for customization, branding and creative uses, starting in small quantities of 50 to large quantities of 50,000 and more.