The right resin can make the difference between a part that simply meets print requirements and one that performs reliably throughout its service life.
Material selection affects nearly every aspect of an injection-molded component—from strength, impact resistance, and dimensional stability to chemical resistance, appearance, processing requirements, and overall part cost.

At MPM, resin selection is considered as part of the complete molding process. We look at the application, part geometry, performance requirements, tooling, and production environment to help determine which material characteristics make the most sense for the project.

What Should Be Considered When Selecting a Resin?

There is rarely one material that is best for every requirement. The right choice depends on how and where the finished component will be used.
Key considerations include:

• Mechanical performance — Strength, stiffness, toughness, impact resistance, and fatigue
• Operating temperature — Continuous heat exposure, peak temperatures, and thermal cycling
• Chemical resistance — Exposure to oils, fuels, cleaners, solvents, chemicals, and moisture
• Environmental conditions — UV exposure, weather, humidity, and outdoor use
• Dimensional requirements — Shrinkage, stability, tolerances, and moisture absorption
• Appearance — Color, texture, gloss, transparency, and surface finish
• Part design — Wall thickness, flow length, ribs, bosses, snap features, and living hinges
• Regulatory requirements — Material certifications or application-specific specifications
• Production economics — Resin cost, cycle time, processing requirements, and expected annual volume
• Evaluating these factors early in the project can help avoid unnecessary material cost, design changes, tooling modifications, and performance issues later in production.

Common and Engineering Thermoplastics

MPM works with a range of thermoplastic materials based on the needs of the application.

Polypropylene (PP)
Polypropylene is one of the most versatile thermoplastics used in injection molding. It is lightweight, cost-effective, and offers excellent chemical resistance along with good fatigue performance.

PP can be an excellent choice for:

• Living hinges and flexible features
• Housings and covers
• Containers and closures
• Fluid-handling components
• Industrial components
• High-volume molded parts

Polypropylene is available in numerous grades, including filled and reinforced formulations, allowing its properties to be tailored to specific applications.

ABS
ABS offers a strong combination of toughness, dimensional stability, processability, and surface appearance. It is frequently considered for housings, covers, enclosures, and other applications where both durability and appearance matter.

Polycarbonate (PC)
Polycarbonate provides excellent impact resistance and good dimensional performance. It is often used for components that require durability, toughness, transparency, or greater temperature capability than many general-purpose plastics.

Nylon (PA)
Nylon is widely used for demanding mechanical components because of its strength, toughness, wear resistance, and ability to perform in structural applications.
Glass-filled and other reinforced nylon grades can provide substantially greater stiffness, strength, and dimensional stability.

Glass-Filled and Reinforced Resins
Reinforcing a thermoplastic with glass fiber or other fillers can significantly change its mechanical and dimensional properties.
Reinforced materials may be selected when a component requires:

• Increased stiffness
• Greater structural strength
• Improved dimensional stability
• Reduced thermal expansion
• Better performance under mechanical loads

Because reinforced materials also affect shrinkage, flow behavior, tool wear, and part design, the material and molding process should be considered together.

High-Temperature & High-Performance Resins
Some applications operate beyond the practical limits of standard thermoplastics. Components located near heat sources, exposed to demanding industrial environments, or required to maintain their properties at elevated temperatures may require a high-performance engineering resin.

Depending on the application, material families may include:

• PEEK
• PEI
• PPS
• High-temperature nylons
• Reinforced high-performance thermoplastics
• Other specialty engineering resins

High-temperature materials can offer combinations of:

• Elevated continuous-use temperature capability
• Strength and stiffness at higher temperatures
• Dimensional stability during thermal cycling
• Chemical resistance
• Hydrolysis resistance
• Wear resistance
• Flame-retardant properties
• Potential metal-replacement opportunities

These materials often require more demanding processing conditions than conventional resins. Mold design, tooling materials, processing temperatures, drying requirements, gate design, and part geometry can all become more critical.

For that reason, high-temperature resin selection should be evaluated as part of the entire molding system—not as an isolated material decision.

Match the Resin to the Application

Specifying a higher-performance material is not always the better solution.

An expensive engineering resin may add capabilities the application does not need, while an under-specified resin can lead to premature failure, dimensional issues, or costly redesigns.

The objective is to find the right balance of performance, manufacturability, and cost.

That may mean choosing polypropylene for a chemically resistant, cost-sensitive component, a reinforced nylon for additional structural strength, polycarbonate for impact performance, or a specialty high-temperature resin for a demanding operating environment.

Material Selection Starts Before Production

Resin behavior influences how a molded part fills, packs, cools, shrinks, and ultimately performs.

Material selection can affect:

• Wall-section recommendations
• Draft and part geometry
• Gate location and flow
• Shrinkage and dimensional tolerances
• Tool construction
• Cooling requirements
• Processing temperatures
• Cycle time
• Long-term part performance

Considering material, part design, and tooling together early in development can help identify potential problems before they reach production.

Not Sure Which Resin Is Right for Your Part?

You don’t need to have every material detail finalized before starting a conversation with MPM.

Send us your part drawing, 3D model, current material specification, performance requirements, or existing molded component. We can review the application and help identify the material and manufacturing considerations that should be addressed before moving forward.

Talk with MPM about your application, material requirements, and injection molding project.