ABS and Polypropylene Comparison

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A glossy black housing with a dish of black pellets beside a translucent hinged box with a dish of clear pellets.

Definition of ABS and Polypropylene Comparison

An ABS and polypropylene comparison is an assessment of acrylonitrile butadiene styrene (ABS) against polypropylene (PP), the two commodity plastics most often considered together for housings, containers, appliance parts and automotive trim. ABS is an amorphous plastic, which means its molecules have no ordered structure, and it is made from three monomers: acrylonitrile for chemical resistance, butadiene rubber for toughness and styrene for rigidity and surface gloss. PP is a semi-crystalline polyolefin, meaning part of its structure forms ordered crystals as it cools, and it is sold as homopolymer, as impact copolymer and in talc-filled or glass-filled compounds. The comparison normally covers density, which is typically 1.04 to 1.06 grams per cubic centimeter for ABS and about 0.90 to 0.91 for PP, together with stiffness, impact strength at room and low temperature, heat resistance, chemical resistance, shrinkage and surface quality. It also covers how each material accepts secondary operations such as painting, chrome plating, pad printing, adhesive bonding and ultrasonic welding. Values are taken from grade datasheets tested to the same ISO methods so that the two materials can be compared on equal terms.

Why This Matters for Your Business

PP usually gives the lower piece price, because it costs less per kilogram and its lower density yields more parts from each kilogram, which makes it the economical choice for containers, closures and clips. ABS costs more but gives a harder, glossier surface and can be painted, chrome plated or bonded directly, while PP needs flame or plasma treatment before paint or print will stay on, which adds a process step, cost and another source of rejects.

ABS also holds tighter tolerances and stays flatter on large parts, which matters for housings whose halves must fit together. PP parts with large flat areas are more prone to warpage and sink marks, and correcting them can mean tool changes and extra trial rounds, so the cheaper material can cost more in development time. In Taiwan's automotive aftermarket, which exports bumpers, grilles and trim to many markets, talc-filled PP is common for bumper covers and plated ABS for grilles.

Related Terms

Plastic Material SelectionShrinkage
Choose ABS when the part needs a rigid, glossy or decorated surface, close dimensional control or assembly by screws, snap fits or bonding, and choose PP when it needs chemical resistance, flexibility, fatigue resistance or the lowest weight. Typical ABS parts are electronic housings, appliance covers, consoles and plated grilles, where appearance and fit come first. Typical PP parts are battery cases, fluid reservoirs and parts with living hinges, which are thin flexible sections that bend thousands of times, where it must resist detergents, oils or repeated flexing. Low-temperature use also guides the choice, because unmodified PP homopolymer becomes brittle at around 0°C, so cold-climate parts need an impact copolymer grade. Where a part needs some of both sets of properties, compounds such as talc-filled PP or blends of polycarbonate and ABS (PC/ABS) are often the better answer.
In most cases it cannot produce parts to drawing, because the cavity was cut oversize for ABS shrinkage, typically 0.4 to 0.7 percent, while PP shrinks by about 1.0 to 2.5 percent. Parts molded in PP from an ABS tool come out undersize and often warp. PP also flows more easily, so it tends to form flash, a thin fin of excess plastic, at vents and parting lines sized for the stiffer ABS melt. A material change usually needs a re-cut cavity or a new tool, followed by a new sample approval.
ABS keeps its shape under load at higher temperatures, with a typical heat deflection temperature (HDT), the temperature at which a loaded test bar starts to bend, of about 80 to 100°C at 1.8 MPa against roughly 50 to 60°C for unfilled PP. Neither material lasts well outdoors in standard grades, since ultraviolet (UV) light makes ABS yellow and brittle and causes PP to chalk and crack. Specify a UV-stabilized grade, or for outdoor ABS parts consider ASA (acrylonitrile styrene acrylate), which has similar properties and better weather resistance.