6 2.2 PS foam types PS foam has been called a “wonder product” because of its unique physical characteristics, including its low specific density, toughness, moisture resistance (Martinelli, 2018). When PS is transformed into foam, it is comprised of over 95% air and is incredibly lightweight. The two types of PS foam, expanded polystyrene (EPS) and extruded polystyrene (XPS), are widely used in food and beverage containers, packaging, toys, floating docks, aquaculture floats, and many other applications. As a buoyant and low-cost material, EPS and XPS have become commonplace in our lives. PS foam has dominated PS production since WorldWar II. Originating from an accidental discovery in a Dow Chemical Company laboratory 1 , PS foam was put to market, and the demand for PS foam quickly grew. During the war effort, PS foam provided an inexpensive building material for aircrafts during a global balsa wood shortage (Breskin, 1947). This new product was a strong material that was 30 times lighter and more flexible than solid PS, and could be easily produced (National Inventors Hall of Fame, 2020). In 1946, the Dow Chemical Company patented Styrofoam®. PS foam can be grouped into two major types; expanded polystyrene (EPS) and extruded polystyrene (XPS). Both materials have low density and low water absorption which make them good thermal insulators. Because of these properties, these materials are often used in construction as insulation (Ibo Osterreichisches Institut Fur Baubiologie Und-Okologie, 2016). PS foam also exhibits good buoyancy properties, and thus is widely used in boat docks and aquaculture floats (Davidson, 2012; ERDC, 2009). The trademark Styrofoam® by the Dow Chemical Company is informally used for all PS foam, although strictly it refers only to “extruded closed-cell” PS foams made by Dow (The Dow Chemical Company, 1946). The physical differences EPS and XPS are shown in Figure 1 and described in the following sections. 1 In the process of trying to make a flexible insulator, scientist Ray McIntire mixed styrene and isobutene in a reactor and heated them, in which he produced a lightweight material known today as PS foam (National Inventors Hall of Fame, 2020). Figure 1: Image of expanded polystyrene (EPS) showing individual cells (left) and extruded polystyrene (XPS), a material without defined PS beads; a material with more consistency (right).