15 - Blank White ATC Cards with 15 White Envelopes to match. These cards are acid-free, lignin-free, buffered and archival quality, and measure 2 1/2 in. x 3 1/2 in. The white envelopes are the perfect size to fit the ATC cards and are acid-free, lignin-free, buffered and also archival quality and measure 2.69 in. x 3.69 in. Fun to create ATC with matching envelopes or just leave the envelopes plain. It is so fun to receive a sealed ATC.