In this activity, learners discover why only some types of plastic can be recycled. The objective of this activity is to increase awareness of recycling polymers through the use of the "three arrow numbering system." Classes of polymers, uses, and physical properties of some thermoplastics are investigated. Safety note: The acetone is extremely flammable and should be kept away from flames. This is an excellent activity to do before "Plastics the Second Time Around," an activity from the same resource (see related resource).