By Ololade Olatunji
June 26, 2026.
You might be designing a new plastic product and you have a wide variety of material options that you can go with. Perhaps you are already running your process with a rather challenging plastic and you wonder if things can be easier. Maybe you’re venturing into injection molding as a newcomer and you’d like to start with materials that are easiest to work with. Here we’ve narrowed down to 5 plastics that are least likely to give you the processing problems. Towards the end we narrow it down even further to the best plastic for new comers into injection molding.
While plastics are widely relied on for their processibility compared to other materials such as steel or wood, not all plastics are equally easy to process. Some plastics require extremely high temperatures, specialized tooling, or strict moisture control to be effectively processed without problems. This is true of plastics such as PTFE and PEEK whose processing temperatures can be as high as …. And polyamides that require extensive drying and moisture control during processing due to their tendency to absorb moisture which could lead to processing problems and defects. Other plastics however, flow smoothly into molds and consistently produce high-quality parts with minimal complications.
Of course certain applications require the use of the more challenging plastics which do eventually pay off in terms of their excellent performance in such applications. This is particularly true for engineering, high performance and specialty plastics. However in applications where these exceptional properties are not a requirement, a manufacturer would do well to choose the less demanding plastics.
Making such a choice can significantly reduce production costs, shorten cycle times, minimize defects, and improve overall manufacturing efficiency. Material selection affects everything from mold design and processing conditions to part quality and long-term performance.
This article presents five of the easiest plastics to work with in injection molding. These plastics are selected on the basis of availability, cost-effectiveness, and their processability. For each one we discuss the strengths and limitations as well as typical applications.
Desirable Properties of Plastics for Injection Molding
First we look at what properties of a plastic makes it easy to injection mold. Then in the following subsections we’ll explore specific plastics and how they meet these criteria to make it onto the list.
Flow Properties
The injection molding process depends on the ability of the plastic in its molten form, to flow along the barrel and into the mold with relative ease. These flow properties are measurable as the melt viscosity. Low melt viscosity reduces the pressure required to push the melt into the mold especially where the product has a complex geometry. The lower pressure also reduces the chances of damage to the mold and likelihood of defects such as short shots, weld lines, and incomplete filling.
Processing Temperatures
The melt viscosity varies with temperature. Generally, above the glass transition temperature, increasing the temperature reduces the melt viscosity up until an optimum point. Therefore a moldable plastic should achieve a desirable melt viscosity at moderate temperature. This minimizes the energy required for heating.
Plastics with lower melting temperatures require less energy and place less stress on machinery and tooling. Cycle times and hence production costs are also reduced using lower melting plastics since the time it takes to heat up and to cool down is reduced.
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Wide Processing Window
This is measured by the glass transition behaviour of the plastic. Even where the processing temperature is relatively high, having a wider processing window reduces the chances of temperature related defects such as burns. There is less need to monitor and tightly control temperature at multiple points of the barrel and the mold or use complex cooling channels. This reduces the cost of tooling.
Minimal Shrinkage
Shrinkage introduces uncertainty into the process. Therefore the higher the tendency of shrinkage, the more challenging the plastic will be to injection mold. Shrinkage occurs during the cooling process and if not adequately accounted for can lead to defects such as warping and dimensional inaccuracies. Although there are methods to account for shrinkage in process design and mold design and it may be advantageous in product ejection, it nonetheless complicates the process and should therefore be minimized.
Therefore in injection molding, when given the choice one would choose plastics with predictable and moderate shrinkage.
Moisture Resistance
A lot of defects and problems that occur in injection molding can be linked to moisture. Bubbles, corrosion, short shot, shark skin, burn marks and others, occur as a result of moisture getting into the process. While a drying stage should always be included before feeding into the injection molding machine, it is best to avoid plastics that are prone to absorbing atmospheric moisture where possible. This reduces the amount of energy and time in drying and the tendencies for moisture related defects and problems.
Therefore based on the above characteristics outlined, the following sub sections lists five plastics that consistently rank among the easiest plastics for injection molding.
1. Polypropylene (PP)
Polypropylene (PP) is the second most used plastics globally. It is often considered one of the easiest and most versatile plastics for injection molding. It is a semi-crystalline thermoplastic that combines excellent moldability with low cost and broad application potential.
Why It Is Easy to Mold
Polypropylene possesses excellent melt flow characteristics with low to medium melt viscosity compared to other plastics. It is typically processed at relatively low temperatures and has a broad processing window that ranges between 180 and 280 °C.
PP is appreciated in injection molding for its ease of mold filling at relatively low injection pressures. It has good mold release properties and relatively short cycle times.
It is also a relatively low cost plastic that’s easy to color so manufacturers are able to meet a broad range of consumer needs with PP. .
Common Applications
- Food containers
- Bottle caps
- Medical packaging
- Automotive trim
- Household storage products
- Consumer goods
Limitations
Despite the relative ease of molding with PP, it tends to show higher shrinkage than some engineering plastics. This must therefore be accounted for in mold design to ensure dimensional accuracy.
2. High-Density Polyethylene (HDPE)
Polyethylene is the most used plastic type globally. Here we list High-Density Polyethylene (HDPE) in particular as it offers broader application in injection molded products than LDPE. HDPE is widely preferred for its excellent durability, chemical resistance, and impact strength. This in addition to its ease of processing and relative low cost. These properties have made it a popular choice in high volume manufacturing.
Why It Is Easy to Mold
HDPE can typically be processed within 180 to 300 °C with medium to high melt viscosity. It gives virtually no moisture problems. It fills the mold well under moderate pressure. Mold release is good and cycle times are short.
Common Applications
HDPE is commonly used for:
- Plastic bottles
- Storage containers
- Pipe fittings
- Fuel tanks
- Toys
- Industrial components
Limitations
HDPE is a bit more prone to shrinkage than PP for example. Shrinkage can be anywhere between 1.5% and 4% depending on exact processing conditions and grade. Therefore this should be properly accounted for to avoid defects such as warping and particularly for thin walled components.
3. Acrylonitrile Butadiene Styrene (ABS)
ABS is one of the most popular engineering thermoplastics used in injection molding or consumer parts. It is particularly preferred for the aesthetically pleasing appearance it can achieve. In addition to ease of processing it also offers strength, toughness, and good surface finish.
Why It Is Easy to Mold
Although it has a slightly shorter processing window than the other plastics listed so far, ABS offers excellent flow properties. It makes up for this by being relatively easy to color and texture resulting in aesthetically pleasing smooth finish. It has good dimensional stability and low shrinkage between 0.4 and 0.8. Its typically processed between 200 to 280 °C and its moderate melt viscosity allows for complex geometries
Common Applications
ABS is used extensively in:
- Consumer electronics housings
- Automotive interiors
- Power tool casings
- Toys
- Appliance components
- Protective equipment
Limitations
ABS has comparatively low resistance to UV light and outdoor conditions. Therefore would require UV stabilizers and other additives or protective coatings to meet the requirement for outdoor applications.
4. Polystyrene (PS)
Polystyrene is one of the easiest plastics to inject mold due to its excellent flow characteristics and low shrinkage.
Although it has been facing bans due to environmental concern and limited recyclability. It has until recently been a popular choice for packaging and consumer products due to its ease of processing and relative low cost.
Why It Is Easy to Mold
Exceptional flow properties with low melt viscosity and processing temperatures that range between 180°C and 260°C. It also has relatively low shrinkage between 0.3 and 0.8. Polystyrene flows well into molds and gets ejected with ease with parts showing good dimensional stability. Its low viscosity particularly allows for thin walled parts and for achieving fine details.
Common Applications
Polystyrene is frequently found in:
- Food packaging
- Disposable cutlery
- Laboratory supplies
- CD cases
- Cosmetic packaging
- Consumer goods
Limitations
A key limitation of PS is its brittleness. Although high impact grades exist. This brittleness prevents its use in its simple form in some applications that require toughness and high impact strength.
5. Polyoxymethylem (POM)
Also commonly referred to as acetal. POM makes it on this list for its wide processing temperature, low affinity for moisture and good flow properties. These make it an attractive option for injection molding where the other properties match the product requirement.
Why It Is Easy to Mold
It is very unlikely to give moisture issues if properly handled. It also allows wide processing windows (190 to 230oC) so you won’t need exceptional temperature monitoring and control. While you can expect some shrinkage, this will occur isotropically in POM. This is more predictable and easier to account for in design calculations.
Common Applications
- Gears and bearings
- Electrical housings
- Switches
- Keyboard keys
- Fuel components in automotives
- Flutes
- Luggage fasteners
- Insulin pens
Limitation
The Key limitation with POM in injection molding is shrinkage. It exhibits mold shrinkage values between 1.5 and 2.5%.
Comparing the Five Plastics
The table below compares the 5 plastics at a glance.
| Material | Typical Processing Temperature Range (°C) | Melt Viscosity* | Mold Shrinkage (%) | Moisture Resistance |
|---|---|---|---|---|
| Polypropylene (PP) | 180–280 | Low to medium | 1.0–2.5 | Excellent; very low water absorption |
| High-Density Polyethylene (HDPE) | 180–300 | Medium to high | 1.5–4.0 | Excellent; virtually unaffected by moisture |
| Polystyrene (PS) | 180–260 | Low | 0.3–0.8 | Good; low water absorption |
| Polyoxymethylene (POM) | 190–230 | Low to medium | 1.5–2.5 | Excellent; very low moisture uptake |
| Acrylonitrile Butadiene Styrene (ABS) | 200–280 | Medium | 0.4–0.8 | Moderate to good; absorbs more moisture than PP, HDPE, and POM |
- Here we have used a qualitative measure of mellt viscosity since the value varies with temperature and grade.
Other Considerations
Although this article has focused on ease of injection molding as the sole criteria. It is important to state that several other factors are considered in material selection. This list is simply to help you make a choice where the options come down to these materials and the only thing left to consider is which is the easiest to inject mold.
Manufacturers should also evaluate mechanical requirements, environmental conditions, exposure to heat, moisture, chemicals, UV radiation, and outdoor environments. Appearance is also important as some applications require transparency, gloss, texture, or specific color capabilities which some plastics may not meet. Regulatory compliance is also key in material selection. Applications such as medical and food-contact products may require compliance with specific regulations and certifications. Material cost, cycle time, tooling requirements, and scrap rates are also factors to consider.
A material that is slightly harder to process may still be the best choice if it provides superior performance in the final application.
Best Plastic for Beginners
To narrow it down even further for companies new to injection molding, polypropylene is often the best starting point. It is relatively low cost, offers excellent processability, it is readily available, It has strong resistance to most chemicals and finished parts are quite durable. Its wide processing window allows manufacturers to achieve consistent results without requiring highly specialized process control systems.
Conclusion
Based on their flow properties, moisture resistance, ease of melting, wide processing window and relatively lower shrinkage compared to other plastics, polypropylene, HDPE, ABS, polystyrene, and POM consistently rank among the easiest plastics for injection molding
Polypropylene stands out as the most versatile and economical option for many applications. HDPE offers outstanding durability and chemical resistance, while ABS provides superior aesthetics and toughness. Polystyrene excels in low-cost, high-volume production, and POM delivers exceptionally good moisture resistance .
