Resins are classified as either natural or synthetic.
Natural resins are the solidified secretions of plants or animals, such as pine resin, natural rubber, or amber. Synthetic resins are generally manufactured, high-polymer substances, usually from petro-chemical materials, and are generally referred to as plastics. Synthetic resins can be either thermoplastic, becoming softer when heated and harder when cooled, or thermosetting, becoming harder when heat is applied. Synthetic resins are easily shaped and suitable for mass production, so they are used as materials for many common products.
