The value of gold-filled is greater than gold-plated because gold-filled has an actual layer of karat gold, not just a microscopic film.
Gold-filled is made by heat- and pressure-bonding a thin layer of karat gold to a brass core. "12/20" gold-filled material is made with 12-karat gold and the gold represents 1/20th (or 5%) of the total weight of the material.
