Vibrant, colorful Pop-Tone response card envelopes or note card envelopes are designed to fit A1 or 4 bar RSVP cards that measure 3 1/2 x 4 7/8 inches. The eye-catching fun envelopes are perfect for enclosing your RSVP cards, thank you note cards, and fun party invitations. Measuring 3.625”x5.125”, this type of envelope is also known as a 4 bar envelope or an announcement, wallet or response envelope. This is the smallest type of envelope that the U.S. Postal Service will deliver with standard postage.