How to choose plastic for injection molding? Comparison of PA6, PA66, PP, PE, ABS

The choice of material is one of the first and most important decisions in any injection molding project. Bad material means complaints, alterations or, in the worst case, a change of mold. The right choice at the design stage saves time, money and nerves throughout the product life cycle.

In this guide, we discuss the five most common plastics used in industrial injection molding: PA6, PA66, PP, PE, and ABS. For each of them, you will find key properties, common uses, advantages and limitations. Finally, a comparison table and a decision tree to help you make a decision for a specific application.

Who is this article for: engineers, constructors, purchasing managers and all those who are faced with the choice of material for a new project or are considering changing the material in an existing one.

Material selection criteria

Before we compare materials, it is worth determining what questions to ask before choosing. A good choice of material is the answer to several key criteria at the same time.

• Mechanical properties – what tensile strength is required? Will the component work under a constant static load or rather exposed to impacts and dynamic loads? Stiffness or flexibility?
• Operating temperature – this is often the decisive criterion. The temperature of continuous operation (not a momentary peak) determines whether PP or ABS is sufficient, whether PA6 or PA66 is needed.
• Chemical resistance – contact with oils, fuels, detergents, acids or alkalis? Each material has a different resistance map and one uncovered medium can destroy an element in a few weeks.
• Dimensional stability – does the component work with metal inserts or does it require precise fits? Hygroscopicity (PA) or high shrinkage (PE) can be a problem.
• Appearance and finish – transparency, gloss, possibility of painting or chrome plating? ABS is the leader here; PA has limitations.
• Price – the cost of the raw material is only a part of the total cost. A material that requires drying, special storage or more difficult processing increases production costs.
• Certification requirements – food contact (FDA, EU 10/2011), medical applications, automotive standards (IATF 16949)? Not every type of every material is allowed.
• Weight of the workpiece – the density of the material is important for large or numerous elements. PP (0.90 g/cm³) is the lightest plastic in this group; PA (1.13 g/cm³) is heavier.

Polyamide PA6

PA6 is one of the most versatile engineering plastics – good strength, decent chemical resistance and low friction in one material.

Key properties: tensile strength 60-80 MPa, continuous operating temperature up to 100°C, good resistance to hydrocarbons and lubricants, low coefficient of friction, abrasion resistance.

Advantages: PA6 is flexible and absorbs impact well – especially in the conditioned state, when the moisture content plasticizes the material. The ease of processing makes injection cycles short and yield good.

Cons: Hygroscopicity is the biggest limitation of PA6. The material absorbs moisture from the environment, which changes the dimensions and mechanical properties. It requires drying (80–100°C, 4–8 h) before injection. In precision applications, swelling must be dimensionally taken into account.

Price: ★★★ ☆☆

Best applications: gears, guides and sliding bushings, automotive components not exposed to temperatures above 100°C, housings and clips, components that require abrasion resistance.

For example: The gear in the car wiper mechanism – PA6 works well thanks to its low friction, good oil resistance and impact resistance at low temperatures in winter.

Polyamide PA66

PA66 is a PA6 with a significantly higher thermal and mechanical bar – justified where PA6 is no longer sufficient.

Key properties: tensile strength of 70-90 MPa, continuous operating temperature up to 120°C (short-term up to 180°C), better creep resistance and higher stiffness than PA6.

Advantages: PA66 is the material of choice wherever higher operating temperature and stability under load are required. The GF30 variants achieve an HDT of over 230°C, making them the automotive standard for components close to the powertrain.

Cons: More expensive than PA6 by 20-40% (raw material). Slightly more difficult to process (higher plasticization temperature). Still hygroscopic, although to a lesser extent than PA6.

Price: ★★★★ ☆

Best applications: engine and under hood components (spigots, filter housings, brackets), high-temperature electrical connectors, structural parts operating under constant load, precision components requiring dimensional stability.

For example: Cooling system connector – PA66 GF30 withstands contact with glycol at 110°C throughout the life cycle of the vehicle, where PA6 would degrade.

Polypropylene PP

PP is the cheapest technical plastic in this group and at the same time one of the most widely used in the world – mainly due to its excellent chemical resistance and very low hygroscopicity.

Key properties: tensile strength 25-40 MPa, operating temperature up to 80-90°C, water absorption below 0.1%, density 0.90 g/cm³ (the lightest of the group), very good resistance to acids, alkalis and detergents.

Advantages: Price, chemical resistance, and food contact approval (FDA, EU) are the three strengths that make PP dominate in packaging, home appliances, and medicine. The lack of hygroscopicity simplifies production logistics – the granules do not need to be dried.

Cons: Significantly lower strength and stiffness than PA. Poor UV resistance without the addition of stabilizers. The lower operating temperature excludes PP from many industrial applications.

Price: ★★ ☆☆☆

Best applications: packaging and containers, household appliances, vehicle interior elements not exposed to high temperatures, disposable medical supplies, components in contact with aggressive chemicals.

For example: The detergent container – PP is resistant to chemicals, cheap for large batches and approved for contact with household chemicals.

Polyethylene PE (HDPE/LDPE)

PE is the cheapest material in the entire group – and at the same time with the narrowest range of technical applications. Its strengths are excellent chemical resistance and flexibility.

Key features: HDPE – strength 20–35 MPa, temperature up to 80°C; LDPE – soft and flexible, temperature up to 60°C. Virtually zero water absorption, density 0.92–0.96 g/cm³.

Advantages: Lowest raw material price, excellent chemical resistance (including to concentrated acids and alkalis), food safe, no hygroscopicity, good elasticity (LDPE).

Cons: Low mechanical strength disqualifies PE from structural applications. Low operating temperature. Soft surface prone to scratches. High processing shrinkage (2-3%) makes precise dimensions difficult.

Price: ★ ☆☆☆☆

Best applications: bottles and containers, caps and caps, flexible films and packaging, technical tubes and hoses, components requiring flexibility and chemical resistance with low mechanical requirements.

For example: Chemical product bottle stopper – HDPE is cheap, content-resistant and safe for the user.

ABS (Acrylonitrile Butadiene Styrene)

ABS is a material that combines good strength with an aesthetic appearance and ease of further processing. It dominates wherever the appearance of the finished product is important.

Key properties: tensile strength 35–55 MPa, high impact strength (up to 20–25 kJ/m² Charpy), operating temperature up to 80°C, processing shrinkage 0.5–0.7% (very low).

Advantages: Possibility of obtaining a very good surface finish (high gloss, electroplating, painting, gluing). Low hygroscopicity and low shrinkage facilitate the production of precise aesthetic elements. Good impact strength even without conditioning.

Cons: Poor chemical resistance – ketones, esters and many solvents attack the ABS. Poor UV resistance without stabilizers. Not suitable for food contact in most applications.

Price: ★★★ ☆☆

Best applications: electronics and device housings, toys, vehicle interior components, parts that require chrome plating or painting, prototypes and components with high aesthetic requirements.

For example: The TV remote control housing – ABS gives high gloss, good impact strength and excellent paint adherence with minimal shrinkage that ensures precise matching of the components.

Comparison table of plastics

* using certified species

Decision tree: which material to choose?

The following questions lead you through the most important selection criteria – answer one by one until you get to the material.

1. What is the maximum temperature of continuous operation?

• Above 100°C → PA66 (or PA66 GF30 at temperatures above 120°C)
• 80-100°C → go to question 2
• Below 80°C → go to question 4

2. Will the component be exposed to harsh chemicals?

(acids, alkalis, detergents)

• Yes → PP (or PE with low mechanical requirements)
• Don’t → go to question 3

3. Is high strength or abrasion resistance required?

• Yes → PA6
• Do not → go to question 5

4. Is the lowest cost a priority?

• Yes → PE (with low requirements) or PP (with chemical requirements)
• Do not → go to question 5

5. Are the appearance and finish of the surface crucial?

(gloss, painting, chrome plating)

• Yes → ABS
• Not → PP (as an economical general choice)

“There is no such thing as the best material – there is only the best material for a specific application.”

Application examples

Gear in car wiper mechanism

Requirements: abrasion resistance, temperature up to 80°C, contact with oil and water, impact resistance at −20°C.
Selection: PA6. Low friction, good chemical resistance and maintaining impact strength in winter are decisive arguments.

Electrical connector housing under the bonnet

Requirements: continuous temperature 110–120°C, contact with engine oil, dimensional stability.
Choice: PA66 GF30. The only material on the list that meets the criteria of temperature and stability in this environment.

Household Appliance Detergent Container

Requirements: contact with chemicals, low cost, large batches, approval for contact with chemicals.
Selection: PP. Excellent chemical resistance, low price and no need to dry the granules.

TV remote control housing

Requirements: good appearance, impact resistance in the event of a fall, possibility of painting, precision of fitting elements.
Selection: ABS. Low shrinkage ensures precision, high gloss possible directly from the mold, good adherence of paints.

Modifications when standard material is not enough

If none of the basic materials meet the requirements, the next step is to modify:

• PA6 GF30 / PA66 GF30 – when significantly higher rigidity, better creep resistance or HDT above 200°C are needed.
• PP + talc – the addition of talc (10-40%) increases the rigidity and HDT of polypropylene, improves dimensional stability while maintaining chemical resistance and low price.
• ABS + PC (blend) – the ABS and polycarbonate blend improves thermal resistance (up to approx. 110°C) and impact resistance at low temperatures. Used in premium electronics and automotive housings.
• PA6 + MoS₂ – the addition of molybdenum disulfide reduces the coefficient of friction by 30–50%. Used in gears, guides and plain bearings where dry friction is a problem.

The 5 most common mistakes when choosing a material

Mistake 1: Choosing the most expensive material “just in case”

PA66 GF30 instead of PA6 in an application where the temperature does not exceed 80°C is an overpayment without any benefit. Each criterion should be verified, not assumed.

Mistake 2: Ignoring operating conditions

A plastic certified for contact with oil at room temperature can fail at 100°C. Always verify chemical resistance at the target temperature, not just at 23°C.

Mistake 3: Underestimating the hygroscopicity of polyamide

The design of the PA6 workpiece with a tolerance of ±0.05 mm without taking into account swelling from moisture is a guarantee of installation problems in the field. Design for conditioned material.

Mistake 4: Skipping Secondary Costs

PA requires drying of the granules before injection (energy, time, risk of overdrying). EP and PP – no. With large volumes, this is a real cost that affects the overall economics of production.

Mistake 5: Choosing a material without consulting the manufacturer

The design may look correct in theory, but turn out to be difficult to process in practice. The geometry of the workpiece, the wall thickness and the surface requirements affect the selection of the material as well as the mechanical properties.

FAQ – frequently asked questions

Which material is the cheapest?

PE (polyethylene) is the cheapest material from the discussed group, PP is in second place. However, the price of the raw material is only part of the total cost – plastics that require drying, longer cycles or more difficult processing may be more expensive to produce despite the lower price of the granules.

Which material is the most versatile?

PP – thanks to the combination of good chemical resistance, low price, lack of hygroscopicity and food contact. However, it is not the answer to the high mechanical or thermal requirements, where PA6 dominates.

Can PA66 be replaced by PA6?

In many applications, yes, as long as the operating temperature does not exceed 100°C and there are no requirements for creep resistance under constant load. The replacement is simple – identical processing shrinkage means that the injection mold remains unchanged.

Which plastics are suitable for contact with food?

PP and PE are commonly used in contact with food (FDA, EU Regulation 10/2011). PA6 and PA66 are only allowed in certified grades – not every commercial grade has such a certificate. ABS is not normally used in contact with food.

How does temperature affect the choice of material?

The operating temperature is often the decisive criterion. At temperatures up to 80°C, all of these materials are available; up to 90°C eliminates PE; up to 100°C – ABS and PP; above 100°C, only PA66 (and its fortified varieties) remains. For temperatures above 150°C of continuous use, high-temperature plastics (PPA, PA46, PEEK) are required.

Is it always worth using fiber-reinforced plastic?

No. GF plastics are more expensive, more abrasive to the mold and more brittle. Reinforcement is justified when significantly higher stiffness, creep resistance or a higher HDT are needed – i.e. when the unmodified plastic does not meet the requirements of the application. If PA6 is enough, PA6 GF30 is an overpayment and shortening the life of the mold.

Summary

There is no one best plastic for injection molding – there is only one that is properly selected for a specific application. PA6 and PA66 dominate mechanical and thermally demanding applications; PP and PE in chemical and economic applications; ABS where aesthetics matter.

Before making a final decision, it is worth answering three questions: what is the maximum operating temperature, what will the element come into contact with and what are the mechanical requirements. The rest is cost optimization and consultation with the manufacturer.

Not sure which material to choose? Contact our technical department – free material advice is a standard part of handling new projects.