The famous Hagner stamp stock sheet system is essentially a looseleaf stamp stockbook
The polyester pockets block ultra violet light which stops fading and repels moisture
Each pocket is bonded to the card with an adhesive rubber strip. This strip flexes and retracts to hold the stamps firmly.
Every part of the Hagner sheet is chemically inactive which means no danger to your stamps, no matter how long they remain in a Hagner sheet.