A thermoplastic (sometimes written as thermoplastic) is a type of plastic made from polymer resin that becomes a homogenous liquid when it hardens when frozen and cooled. When frozen , it becomes a thermoplastic glass-like and breaks bones. This feature , to which the material is assigned its name, is the opposite. That is , it can be repeated , rescheduled , and repeatedly frozen. This makes quality thermoplastics recyclable . There are several types of thermoplastics , with each type of crystal having different organization and density. Currently the most commonly used types are polyurethane , polypropylene , polycarbonate and acrylic. Celluloid , considered the first thermoplastic , showed its presence in the mid-1800s and ruled the industry for almost 100 years . During its peak production , it was used as an alternative to ivory. Today , it is used to choose the guitar. Sometimes , thermoplastics are confused with thermosetting plastics. Although they may sound the same , they actually have very different characteristics. Thermoplastics can be dissolved in a liquid and cooled to a solid state , the chemical being reduced after heating the watermelon. Ironically , however, thermosetting plastics tend to be more durable when allowed to cool than many thermoplastics.