Acid free, sulphur free and PH neutral. These paper 2x2 Coin Envelopes provide safe and economical storage for your coin collection. The envelope flaps are plain and do not have adhesive gum. Available in a variety of colors so that you can organize by coin denomination. Manufactured by Guardhouse, a trusted brand in coin collecting. Are you using Acid Free and PH Neutral paper? There are a wide variety of 2 x 2 paper coin envelopes available but most of them are not specifically designed for safely storing your coin collection.