The Prims & Flourish specialty A4 invitation envelopes measure 4 1/4 x 6 1/4 inches and are made of acid-free paper for long-lasting quality. This set comes in 6 adorable colors, making it a cheery choice for sending birthday parties, baby showers, and wedding invitations. Each envelope is sized perfectly for your RSVP cards, invitations, announcements, and notes. The envelope is easily sealed by a water-soluble gum on the flap that requires a little moisture to activate. Great for social invitation purposes, the A4 size is also a great reply envelope that easily fits inside A6, A7, A8, A9, and A10-sized envelopes.