A custom peel testing device has been developed to measure adhesion strength of flexible thin film layers. The device overcomes the inherent problems of traditional peel machines that are associated with inaccurate peel angle definition and complex sample clamping. To demonstrate its performance, we have compared peel adhesion of currently used paper-based and polymer-based banknotes. Polymer banknotes have shown higher peel strength, which may yield greater durability and ensure increased lifetime in intensive use during circulation.