Pokemon Mewtwo 4-Pocket Portfolio - Rules of Play says:

Keep your valuable cards safe and organized with Ultra PRO's 4-Pocket Portfolio. Made in California, USA, and featuring Mewtwo from Pokémon Trading Card Game, these portfolios are ideal for sorting, organizing and storing trading cards. Holds 40 collectible cards single-loaded or 80 double-loaded. Each Portfolio includes 10 high-clarity, archival-safe pages.