Adhesives are polymer materials that are used to join dissimilar materials. Adhesives may be classified in many ways, e.g. by mode of application and setting, chemical composition, cost, and suitability for various adherents and end products. The term “pressure sensitive adhesive” (PSA) is used to describe adhesives that are permanently tacky in dry form at room temperature. The most common pressure sensitive adhesives are acrylics, natural rubber/resin, and synthetic rubber/thermoplastic rubber.