EPS (expanded polystyrene) and EPP (expanded polypropylene) are two types of expanded plastic foam. They are both light, durable and inexpensive to manufacture. Both find extensive use in packing, insulation, model-making and various types of safety gear. The two plastics have different physical properties, making EPS more suitable for some applications and EPP for others. Other differences include the chemicals used in their manufacture and their relative environmental impact.
Polystyrene is one of the commonest plastics in use today. EPS is used to make packaging for delicate items, as its foam structure absorbs energy, making it impact resistant. Because of this, EPS also finds use in safety equipment such as cycle helmets and infant car seats. Because of its good insulating properties, EPS is used for food and beverage containers, especially for hot items, as well as in coolers and as building insulation.
Unexpanded beads of polystyrene are placed in a hopper, where they are expanded using a small quantity of a blowing agent -- typically pentane -- and jets of steam. The steam causes the pentane to boil, resulting in the polystyrene beads becoming filled with cavities containing boiling pentane, expanding each bead in size by around 4000 percent. The pentane liquefies as it cools, leaving air-filled bubbles throughout each bead. The expanded beads are then fed into a mold to be pressed together into a single block of EPS.
EPP is used in similar applications as EPS, including packing material, insulation and safety gear. EPP can be used to make microwaveable food containers and is heat resistant. EPP is more elastic and less brittle than EPS, which is easily dented permanently, while EPP springs back into shape. EPS tends to crack, snap or crumble under stress, making it unsuitable for items that must withstand multiple impacts such as automotive bumpers. EPP, on the other hand, is used extensively in the automobile industry. Unlike EPS, EPP can be used for furnishings. It is more fire resistant than EPS and can be used for exposed surfaces, whereas EPS building insulation must be covered with Sheetrock or a similar nonflammable material.
The exact manufacturing method for EPP is a proprietary process. EPP differs from EPS in that it does not need a blowing agent; this reduces its environmental impact somewhat, since the blowing agents for EPS generally have a negative environmental impact. EPP can also be completely recycled, a process that is significantly less feasible for EPS.