Paper Accents Envelopes are perfect for greeting cards, invitations, letters, and more. Let someone know that they have received something special before its even opened. These envelopes are acid-free, lignin-free, buffered and archival quality. Flat Flap. A2. For use with 4 1/4 x 5 1/2 inch cards. Actual envelope size: 4 1/2 x 5 3/4 inch. #145 Sea Blue. 25 pc.