ABS vs PP

What ABS is

ABS is a two-phase polymer, a rigid styrene-acrylonitrile matrix with butadiene rubber dispersed through it. The matrix gives stiffness and a hard surface, the rubber phase absorbs impact energy, which is why its own relative-property chart scores it 45 on stiffness and 70 on impact toughness against PP’s 25 and 55. It molds at low pressure, holds fine texture, and is the only one of the two that takes paint and electroless plating without a primer, scoring 85 on cosmetic finish on its own chart, an axis PP’s chart does not even carry. Its limits are heat and chemical exposure: it softens above roughly 90 °C and its own chart rates chemical resistance at just 35, against PP’s 95.

What PP is

Polypropylene is a semi-crystalline polyolefin with the lowest density of the two (0.90 g/cm³ against ABS’s 1.04) and by far the best chemical resistance of any common molding plastic, resisting almost every acid, base and solvent a product meets in normal use. It absorbs essentially no water (under 0.02 % against ABS’s 0.3 %) and its own chart scores fatigue life at 95, the property behind the only real living hinge among common molding plastics, an axis ABS’s own chart does not carry at all. The trade-off is stiffness and finish: its flexural modulus is little over half of ABS’s, its own chart rates impact toughness lower too (55 against 70), and nothing bonds to it without a surface treatment first.

A heat deflection figure that looks like a contradiction and is not

Read on its own, PP’s 100 °C heat deflection figure looks higher than ABS’s 88 °C, which would suggest PP tolerates more heat. The two numbers are not measured the same way: ABS’s figure is taken under the higher 1.8 MPa test load, PP’s under the lower 0.45 MPa load, so a lower-stress part of PP is being compared with a higher-stress part of ABS. Each material’s own relative-property chart, which is not tied to either raw test load, already reflects this: it scores PP’s heat resistance at 45 against ABS’s 35, a real but narrower gap than the raw 88-versus-100 figures alone would suggest to a reader moving quickly between the two pages.

ABS against PP

Which one, for which part

• A painted, plated, or cosmetically finished enclosure or bezel is ABS’s case: it is the only one of the two that plates and paints without a primer, and it scores 85/100 on cosmetic finish against an axis PP’s own chart does not carry.
• A part that has to survive acids, bases, or solvents in normal use is PP’s case: it scores 95/100 on chemical resistance against ABS’s 35.
• A living hinge, or a feature flexed thousands of times is PP’s case: it is the only common molding plastic engineered for a real living hinge.
• A structural enclosure that has to carry load or survive impact favours ABS: its flexural modulus is nearly double PP’s and its impact toughness score is 70 against 55.
• A cost-sensitive, high-volume part with no cosmetic requirement favours PP: it is rated “very low” cost against ABS’s “low,” and it needs no drying step before molding.
• Tight first-shot tolerances on a new tool favours ABS: its shrinkage is lower and near-isotropic, while PP’s is direction-dependent and continues moving for up to 24 hours after ejection, so parts have to be measured the next day, not off the press.

Our status

Trumould molds both ABS and PP in-house on the same press range. ABS is also available through our CNC machining and 3D printing capabilities; PP is available through injection molding and CNC machining, not 3D printing. Send the part, what it has to survive, and target volume, and the quote states which of the two is recommended and why, not just a price for whichever one you asked about first.