Expanded polystyrene foam, commonly known as Styrofoam, is a widely used material. This lightweight and versatile substance appears in various products, from coffee cups to protective packaging. A common question is how it interacts with water. This article explores how expanded polystyrene foam behaves in the presence of moisture and the underlying scientific principles that govern its properties.
How Styrofoam Reacts to Water
When expanded polystyrene foam contacts water, it does not readily absorb the liquid. Instead, water beads up and rolls off its surface, rather than soaking into the material. This means its insulating ability, buoyancy, and structural integrity remain largely unchanged even with surface moisture. Expanded polystyrene foam will not swell, degrade, or dissolve when immersed in water.
The Science Behind Its Water Resistance
The water resistance of expanded polystyrene foam stems from its composition and structure. The material is primarily derived from polystyrene, a type of plastic. Polystyrene itself possesses a hydrophobic nature, meaning it naturally repels water molecules. This property is amplified by the foam’s “closed-cell” structure.
The foam consists of countless individual, sealed cells, which are filled primarily with air, often making the material up to 98% air by volume. These sealed air pockets prevent water molecules from penetrating the material’s interior. Unlike materials like paper or wood, which have open structures that allow water to be absorbed into their fibers, the tightly packed, non-interconnected cells of expanded polystyrene foam act as barriers to moisture.
While highly water-resistant, expanded polystyrene foam is not entirely waterproof. Some types, like expanded polystyrene (EPS), can absorb a small amount of water over extended periods due to tiny gaps between fused beads. Extruded polystyrene (XPS), often branded as Styrofoam, offers superior moisture resistance.
Everyday Uses of Water-Resistant Styrofoam
The water-resistant properties of expanded polystyrene foam make it valuable in many everyday applications. Its ability to repel moisture is frequently utilized in packaging, where it safeguards goods from dampness during transit and storage. This material is also widely employed as an insulating agent in products such as portable coolers and within building materials, where its resistance to moisture helps maintain thermal performance in potentially damp environments. The material’s consistent buoyancy in water further extends its utility. Expanded polystyrene foam is a common component in various flotation devices, including dock floats and buoys, because it resists waterlogging and maintains its ability to float even if punctured.