Linn’s Stamp News says:
Stock books are useful additions to any kind of stamp collection. They keep stamps safe and require no hinges or mounts. Stamps are held in place with strips of glassine paper or clear plastic strips, depending on the style and brand.
A stock book is a good place to safely store new issues until such time as the appropriate album supplement is acquired. With reasonable care, a stock book will last a very long time. The key to keeping them in good shape is to not overstuff them. Don’t overload the strips of glassine or clear plastic because the glassine will tear or the clear strips will pull away from the backing board.