Polycarbonate is the stiffer, tougher and more heat-resistant of the two, and it comes out of the mould glass-clear at any wall thickness; polypropylene is a quarter lighter, cheaper per kilogram, moulds without a dryer, and takes the bases and polar solvents that crack polycarbonate.
Before putting any two figures side by side, check that they were measured the same way. Polycarbonate’s melt flow is quoted at 300 °C under 1.2 kg and polypropylene’s at 230 °C under 2.16 kg, so those two numbers never belong in one column.
What Is Polycarbonate
Polycarbonate is an amorphous engineering thermoplastic built from bisphenol A and a carbonate source. Being amorphous, it has no melting point: its producers publish a glass transition temperature of 144 °C instead.
It is sold on melt volume-flow rate at 300 °C / 1.2 kg, and in the main brands the leading digits of the grade number encode that viscosity. The easier-flowing grades are the less tough ones.
It is bought for transparency plus heat resistance: glazing and automotive lighting, lenses and light guides, transparent housings, electrical and electronic parts, medical devices and labware. We ship it as virgin and modified granules.
What Is Polypropylene
Polypropylene is a semi-crystalline commodity polyolefin at about 900 kg/m³ (ISO 1183), sold on a melt flow rate measured at 230 °C under 2.16 kg.
It comes in three families — homopolymer, random copolymer and impact copolymer — and which of the three is quoted decides most of what any comparison against polycarbonate can say. Only two of them are ever really in the running: a clarified random copolymer where the part has to be seen through, and an impact copolymer where it is a housing, a lid or a crate.
Between them the three families cover packaging film, food containers and closures, housewares, pails and crates, woven sacks and automotive interior parts — the bulk of the polypropylene grades traded by the container load.
The Difference Between Polycarbonate and Polypropylene
Polycarbonate leads on stiffness, notched impact, heat and optical clarity. Polypropylene leads on weight, resin cost, resistance to bases and polar solvents, flex life and processing simplicity.
Strength and Impact Resistance
Among unfilled moulding grades polycarbonate is the stronger material on both counts, and impact is where the gap is widest. Notched Charpy at 23 °C (ISO 179-1/1eA) reads 65 kJ/m² for a general-purpose polycarbonate against 4 to 8 kJ/m² for polypropylene homopolymers and 5.5 to 13 kJ/m² for impact copolymers.
Yield stress separates them by less: 65 MPa for polycarbonate, 35 to 38 MPa for homopolymer, 26 to 27 MPa for impact copolymer (ISO 527).
Cold widens the gap again. Polycarbonate still tests 15 kJ/m² notched at −30 °C, above where impact copolymers sit at −20 °C (3.5 to 4.5 kJ/m²) and above homopolymer at room temperature.
Stiffness and Fatigue
Polycarbonate is the stiffer material by roughly 1.5 to 1.8 times, and polypropylene survives repeated flexing. Flexural modulus is 2,350 MPa for polycarbonate (ISO 178) against 1,300 MPa for a homopolymer and 1,450 to 1,500 MPa for impact copolymers.
A clarity random copolymer measures 620 MPa on the ASTM flexural test against 2,340 MPa for polycarbonate, so a clear polypropylene part is about a quarter as stiff as the polycarbonate one it replaces. Hinged lids, snap fits and integral hinges are polypropylene parts; polycarbonate is not specified for one.
Hardness and Scratch Resistance
Polycarbonate is harder on every scale, and how much harder is an artefact of the scale chosen. Ball indentation (ISO 2039-1) puts it at 115 N/mm² against 53 MPa for an impact copolymer, a factor of 2.2; Rockwell R (ASTM D785) puts it at 118 against 107 for a homopolymer and 85 for a random copolymer, eleven points apart on a 150-point scale.
Bare polycarbonate loses 10 mg per 1,000 cycles on Taber CS-17 under a 1 kg load (ASTM D1044), so lenses and glazing are bought hard-coated, and a coated sheet can no longer be thermoformed. Polypropylene is softer; it marks where polycarbonate scratches, and on an opaque part a mark is rarely a defect.
Heat Resistance
At the same load and standard polycarbonate holds its shape about 70 °C hotter: heat deflection temperature 124 °C against 55 °C for a polypropylene homopolymer at 1.80 MPa (ISO 75). Drop the load to 0.45 MPa and polycarbonate reads 137 °C while polypropylene grades read 75 to 127 °C, narrowing the gap to somewhere between 10 and 35 °C.
The melting point of polypropylene, 160 to 165 °C, is not a service temperature at all — it sits about 110 °C above the same grade’s heat deflection temperature at 1.80 MPa.
For continuous service, polycarbonate carries a UL 746B relative temperature index of 125 °C at 1.5 mm on tensile strength. No polypropylene producer publishes an equivalent index for these grades, so a continuous-use comparison has to be made on heat deflection temperature at a stated load.
Chemical Resistance
Neither one is the inert material; the answer flips by chemical family, so the fluids the part actually sees decide it. The two sets of ratings below are not generated the same way — polypropylene’s come from ASTM D-543 standard reagents at 21 °C and 49 °C, polycarbonate’s from six days of exposure under an applied outer-fibre strain at 23 °C — so read them as direction rather than as specification.
| Medium | Polypropylene | Polycarbonate |
|---|---|---|
| Sodium hydroxide | satisfactory at 60 % | not resistant at 1 % |
| Acetone | satisfactory at 21 and 49 °C | swells |
| Methanol | satisfactory | not resistant |
| Ethanol, isopropanol | satisfactory | resistant |
| Dilute mineral acids, 10 % | satisfactory | resistant |
| Heptane, white mineral oil | not recommended | resistant |
| Toluene, xylene, chlorinated solvents | not recommended | swells or dissolves |
Polycarbonate fails by environmental stress cracking, so a low-stress part can pass an exposure that a stressed one fails. Hot water hydrolyses it as well.
Polypropylene is not stress-crack sensitive in that strict sense; what looks like stress cracking in bleach is oxidative degradation of the polymer. Polycarbonate is not resistant to standard petrol and diesel, and polypropylene’s resistance improves with the highest practical molecular weight, which means the lowest melt flow rate the part can be moulded in.
Transparency
Polycarbonate is water-clear as moulded at any wall thickness, and polypropylene reaches usable clarity only as a clarified random copolymer in a thin section. Luminous transmittance for polycarbonate is 89 % at 1 mm and 87 % at 4 mm (ISO 13468-2), with haze below 0.8 % at 3 mm. Clarified polypropylene random copolymers measure 7 to 11 % haze in a 1 mm wall (ISO 14782), so polycarbonate is clearer through three times the section.
The same random-copolymer family measures 1.2 % haze as a 50 µm cast film, and an unclarified grade publishes no haze figure at all — so what clear polypropylene can do is a statement about the additive package and the wall thickness.
Density and Weight
Polypropylene is lighter by a quarter: 900 kg/m³ against 1,200 kg/m³ on the same standard (ISO 1183). The same part geometry therefore holds 25 % less mass in polypropylene, and since resin is bought by the kilogram while the part is a volume, that ratio applies to the resin bill before any price difference is counted.
Moisture Absorption and Drying
Polycarbonate has to be dried before moulding and polypropylene does not. Polycarbonate takes up 0.30 % water at saturation and 0.12 % at 23 °C and 50 % relative humidity (ISO 62), and it must be below 0.02 % residual moisture for injection moulding and 0.01 % for extrusion — typically 2 to 4 hours at 120 °C in a modern dryer, and up to 12 hours in an older one.
The dryer, its energy and its residence time sit on the polycarbonate side of any cost comparison.
Food Contact and Sterilization
In the United States both materials are cleared for food contact, in the EU only polypropylene is, and at the high autoclave setting only polypropylene survives. In the US, polycarbonate is cleared under 21 CFR 177.1580 with one excluded article class — infant feeding bottles and sippy cups — and polypropylene under 21 CFR 177.1520.
In the EU, Regulation (EU) 2024/3190 prohibits the use of bisphenol A in the manufacture of food-contact plastics. It entered into force on 20 January 2025, the general transitional deadline for placing such articles on the market passed on 20 July 2026, and BPA has been deleted from the positive list of authorised monomers.
No derogation covers polycarbonate, and a “BPA-free polycarbonate” does not answer it, because the resin cleared under the US section is defined as the condensation product of bisphenol A.
Both take the standard 121 °C steam cycle, and polypropylene also withstands the 134 °C fast autoclave setting that polycarbonate’s producer rules out, capping steam at 125 °C.
Under gamma sterilisation, polycarbonate takes 10 to 20 doses of 28 kGy before strength falls appreciably, yellowing a little more each time, while polypropylene embrittles unless it is stabilised against radiation. Polypropylene is also transparent to microwave energy and is the material used in microwaveable containers.
Molding and Surface Treatment
Polycarbonate moulds hot, dry and slow, polypropylene cool and fast, and surface treatment goes the other way round. Polycarbonate melt temperature runs 280 to 320 °C with the mould at 80 °C or above, against 220 to 260 °C melt and a 30 to 40 °C mould for a polypropylene homopolymer.
A polypropylene surface is impervious to solvents and has to be flame- or corona-treated before ink, paint or adhesive will hold.
Polycarbonate takes paint and adhesive as moulded, with one condition attached. A solvent-borne system can swell it or start stress cracks depending on the solvent and the flash-off, and paints containing turpentine are out.
How to Choose the Right One
A part that sees cleaning agents or bases, needs an integral hinge, is priced by weight or goes into a microwave or a 134 °C autoclave is a polypropylene part. A part that has to survive impact below freezing, stay stiff while hot, be glass-clear through a thick section or take repeated gamma sterilisation is a polycarbonate part.
The choice is only real for a part that could plausibly be moulded in either — a clear housing or container, labware, a lid, a hard shell. If the part is an opaque housing, the comparison to run is usually polypropylene against ABS instead.
On cost, polycarbonate is the more expensive resin per kilogram, and the gap widens per part once the density difference and the drying step are counted.
Four datasheet lines decide most real cases: notched impact at the part’s lowest service temperature, heat deflection temperature at a stated load, light transmittance at the part’s own wall thickness, and water absorption.
Outdoors, both materials need a stabiliser package, and how long a polypropylene part lasts outdoors is a question about that package. Polycarbonate’s UV stabilisation is a grade attribute encoded in the type number, so an unstabilised general-purpose grade ships by default unless the UV grade is ordered.
Both are recyclable, and recycled polypropylene is traded in far larger volume, which matters where the part carries a recycled-content target.