Material selection for a molded part is made once and locked in by tooling. Change your mind after the mold is cut and shrinkage differences alone may make the tool unusable, since cavity dimensions are sized around the specific resin’s shrink rate.<\/p>\n\n\n\n
That makes it worth more analysis than it usually receives. Four materials cover a large proportion of molded engineering parts, and each has a domain where it clearly wins.<\/p>\n\n\n\n
This guide compares them on the properties that actually decide the choice, then covers the practical points that catch people out.<\/p>\n\n\n\n
ABS<\/strong><\/p>\n\n\n\n Acrylonitrile butadiene styrene, an amorphous thermoplastic and one of the most widely used molding materials.<\/p>\n\n\n\n Strengths.<\/strong> Molds easily with good flow and low shrinkage, produces good surface finish, takes texture and paint well, is readily bonded and machined, has decent impact resistance, and is inexpensive. Dimensionally stable and forgiving of design imperfections.<\/p>\n\n\n\n Weaknesses.<\/strong> Modest temperature resistance, poor UV resistance without stabilisation, and limited chemical resistance, particularly to solvents.<\/p>\n\n\n\n Typical uses:<\/strong> consumer product housings, enclosures, automotive interior trim, toys, appliance components, anything where appearance and cost matter and the environment is benign.<\/p>\n\n\n\n Why it is the default.<\/strong> ABS is forgiving. It fills easily, shrinks predictably, tolerates imperfect wall thickness better than most, and finishes well. Where requirements do not rule it out, it is usually the sensible starting point.<\/p>\n\n\n\n Polycarbonate<\/strong><\/p>\n\n\n\n An amorphous engineering thermoplastic known for exceptional impact resistance and optical clarity.<\/p>\n\n\n\n Strengths.<\/strong> Outstanding impact strength across a wide temperature range, natural transparency, good heat resistance, and good dimensional stability.<\/p>\n\n\n\n Weaknesses.<\/strong> Notch sensitive, meaning sharp internal corners substantially reduce its impact performance. Poor resistance to many solvents and some cleaning agents, which can cause stress cracking. Prone to scratching. Requires thorough drying before molding, since moisture causes degradation. Higher cost than ABS.<\/p>\n\n\n\n Typical uses:<\/strong> safety equipment, transparent covers and lenses, electrical housings, medical device components, anything requiring impact resistance or clarity.<\/p>\n\n\n\n The notch sensitivity point matters practically.<\/strong> Polycarbonate’s impact performance depends heavily on avoiding stress concentrations. Generous radii at internal corners are not a refinement, they are necessary to realise the material’s advantage.<\/p>\n\n\n\n PC-ABS<\/strong><\/p>\n\n\n\n A blend combining properties of both.<\/p>\n\n\n\n Strengths.<\/strong> Better impact and heat resistance than ABS, better processability and lower cost than PC, reduced notch sensitivity compared to PC, and good surface finish.<\/p>\n\n\n\n Weaknesses.<\/strong> Not as strong or heat resistant as PC, not as cheap as ABS. Chemical resistance is moderate.<\/p>\n\n\n\n Typical uses:<\/strong> automotive interior and exterior components, electronics housings, applications where ABS is marginal on impact or temperature but PC is more than required.<\/p>\n\n\n\n Why it exists.<\/strong> PC-ABS occupies genuine middle ground. It is not a compromise in the pejorative sense but a practical answer where ABS falls short and PC is over-specified or difficult to process for the geometry.<\/p>\n\n\n\n Nylon<\/strong><\/p>\n\n\n\n Polyamide, a semi-crystalline engineering thermoplastic. PA6 and PA66 are the common grades.<\/p>\n\n\n\n Strengths.<\/strong> Excellent mechanical strength and stiffness, good wear resistance and low friction, good chemical resistance particularly to oils and fuels, and good heat resistance. Glass-filled grades are substantially stronger again.<\/p>\n\n\n\n Weaknesses.<\/strong> Absorbs moisture, which changes both dimensions and mechanical properties. Higher shrinkage than amorphous materials, and shrinkage is directional in filled grades, making warpage harder to control. Requires thorough drying before molding. Poor UV resistance without stabilisation.<\/p>\n\n\n\n Typical uses:<\/strong> gears, bearings, bushings, mechanical components, under-bonnet automotive parts, electrical connectors, anything requiring strength, wear resistance or chemical resistance.<\/p>\n\n\n\n The moisture point is the main design consideration.<\/strong> Nylon absorbs moisture from the atmosphere and swells as it does. Parts change dimension between molding and equilibrium, and mechanical properties change with them. For precision parts this must be designed around, and it is a frequent source of surprise for engineers new to the material.<\/p>\n\n\n\n Comparison<\/strong><\/p>\n\n\n\n Selecting by Requirement<\/strong><\/p>\n\n\n\n Impact resistance is the driver:<\/strong> PC, or PC-ABS where PC is over-specified.<\/p>\n\n\n\n Transparency is required:<\/strong> PC among these four, though acrylic and some other materials are alternatives depending on the application.<\/p>\n\n\n\n Wear, friction or mechanical loading:<\/strong> nylon, likely glass-filled.<\/p>\n\n\n\n Chemical or fuel exposure:<\/strong> nylon.<\/p>\n\n\n\n Appearance and cost:<\/strong> ABS.<\/p>\n\n\n\n Elevated temperature:<\/strong> PC or nylon, with PC-ABS adequate for moderate cases.<\/p>\n\n\n\n Outdoor exposure:<\/strong> none of these without UV stabilisation. Specify a stabilised grade or design in protection.<\/p>\n\n\n\n Tight dimensional tolerance:<\/strong> ABS or PC, since nylon’s moisture absorption complicates it.<\/p>\n\n\n\n Moldability Differences<\/strong><\/p>\n\n\n\n Material choice affects tooling and processing, not just part properties.<\/p>\n\n\n\n ABS<\/strong> is forgiving. It fills easily, shrinks predictably at a low rate, and tolerates less-than-ideal wall thickness. Tooling is straightforward.<\/p>\n\n\n\n PC<\/strong> has higher viscosity and needs higher melt temperatures. It requires thorough drying, since moisture causes hydrolytic degradation. Molded-in stress is a concern, and annealing is sometimes required.<\/p>\n\n\n\n PC-ABS<\/strong> processes more easily than PC while retaining most of the property advantage over ABS.<\/p>\n\n\n\n Nylon<\/strong> flows well but shrinks more than amorphous materials, and shrinkage in glass-filled grades is directional, following fibre orientation. This makes warpage prediction harder and increases the value of flow simulation. Drying is essential.<\/p>\n\n\n\n The practical implication is that switching material after tooling is designed is often impossible. Cavity dimensions are sized to the specific resin’s shrink rate, so a change to a material with different shrinkage may require tool modification or a new tool. Settle material before steel is cut.<\/p>\n\n\n\n Filled and Modified Grades<\/strong><\/p>\n\n\n\n Each of these materials is available in numerous grades, and the differences between grades can exceed the differences between base materials.<\/p>\n\n\n\n Glass fibre<\/strong> substantially increases strength and stiffness and reduces shrinkage, at the cost of surface finish, impact resistance and increased tool wear from abrasion.<\/p>\n\n\n\n Mineral fillers<\/strong> improve dimensional stability and reduce cost, with less impact on surface finish than glass.<\/p>\n\n\n\n Impact modifiers<\/strong> improve toughness at some cost to stiffness.<\/p>\n\n\n\n UV stabilisers<\/strong> are necessary for outdoor use in all four materials.<\/p>\n\n\n\n Flame retardant grades<\/strong> are required for many electrical applications and change processing behaviour, sometimes considerably.<\/p>\n\n\n\n Specify the actual grade, not just the material family. “Nylon” is not a specification. A specific PA66 grade with a defined glass content is.<\/p>\n\n\n\nPropri\u00e9t\u00e9<\/strong><\/td> ABS<\/strong><\/td> PC<\/strong><\/td> PC-ABS<\/strong><\/td> Nylon<\/strong><\/td><\/tr> R\u00e9sistance aux chocs<\/td> Bon<\/td> Excellent<\/td> Very good<\/td> Bon<\/td><\/tr> Heat resistance<\/td> Mod\u00e9r\u00e9<\/td> Bon<\/td> Bon<\/td> Bon<\/td><\/tr> R\u00e9sistance chimique<\/td> Limit\u00e9e<\/td> Limit\u00e9e<\/td> Mod\u00e9r\u00e9<\/td> Bon<\/td><\/tr> Dimensional stability<\/td> Bon<\/td> Bon<\/td> Bon<\/td> Moisture sensitive<\/td><\/tr> Transparency<\/td> Non<\/td> Oui<\/td> Non<\/td> Non<\/td><\/tr> Moldability<\/td> Excellent<\/td> Requires care<\/td> Bon<\/td> Requires care<\/td><\/tr> R\u00e9tr\u00e9cissement<\/td> Faible<\/td> Faible<\/td> Faible<\/td> Higher, directional<\/td><\/tr> Finition de la surface<\/td> Excellent<\/td> Bon<\/td> Very good<\/td> Mod\u00e9r\u00e9<\/td><\/tr> Relative cost<\/td> Lowest<\/td> Highest<\/td> Middle<\/td> Middle to high<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n