Plastic Mold Design Checklist – Guidelines to Cover with an Injection Molder

Poor specification & improper material selection is the leading cause of failure in plastic injected molded parts, followed by improper plastic injection mold design and processing practices.

Having an understanding of plastic injection mold design basics can help you avoid part defects, such as mold warpage and gas trap (formerly known as mold burns), voids, short shots and various other incorrect design flaws, which can result in expensive & time-consuming product callbacks and part rework.

Below is a plastic mold design checklist to cover with your plastic injection molder.

Resin Requirements

The first thing to know when seeking out plastic injection mold design assistance is what type of resin your application requires – commodity or engineering grade. The type of resin you require is based on numerous factors – from part environmental conditions to load bearing.

Remember, there are over 30,000 resin formulas available so it’s important to know your environmental requirements so you can choose your engineering resin wisely. There is a wide distance in mechanical and chemical properties in this menu of choices. Improper selection of plastic resins can result in many product failures in the field use of the finished product.

Next, you will need to provide information on whether you have your own chosen resin manufacturer or if you need one. If you have your own chosen resin manufacturer, be sure to provide all MSDS information to the plastic injection molder.

Part Specifications

Part specifications you’ll want to detail include:

  • Part Size
  • Part Geometry
  • Wall Thickness
  • Dimensional Tolerances
  • Number of Cavities
  • Presence of Sharp Corners or Ribs
  • Presence of Holes and Cores
  • Applicable Inserts
  • Electrical Requirements
  • Approximate Part Life Expectancy
  • Other Needed Secondary Options


Strength requirements play a significant role in plastic injection mold design. Strength requirements to take into account include:

  • Load Bearing
  • Impact Absorption
  • Stress Resistance
  • Stiffness
  • Impact
  • Tensile Strength

Operating Environments

Operating environments is a key component in plastic injection mold design. Environmental factors that can affect your part may include:

  • Temperature
  • Moisture
  • Chemicals
  • Corrosion
  • UV Radiation
  • Material Compatibility
  • Flame Retardation


Depending on the application of your part there may be certain aesthetic requirements, such as:

  • Color
  • High Clarify Transparency
  • Smoothness
  • Texture
  • Matte
  • High Gloss
  • Marking/Logos
  • Date Codes

Post-Molding Services

Depending on part requirements, you may need post-molding services, such as:

  • Heat treating
  • Surface finishing
  • Welding
  • Ultra-Sonic Welding

Agency Approval(s)

Many plastic parts must pass private and/or government regulations. It’s important to provide the appropriate compliance requirements for your part.

Compliance agencies may include:

  • FDA
  • ISO
  • USDA
  • IEC
  • RoHS
  • UL
  • MIL


  • Budget
  • Production Quantities
  • Turnaround Time

The more information you can provide to a plastic injection molder upfront, the higher your chances are of receiving a quality product that’s produced right the first time.

U.S. Plastic Injection Molder Specializing in Complex Projects for Mission-Critical Parts

Plastic Molded Concepts is a U.S. plastic injection molder specializing in engineering resins. We provide all-inclusive plastic injection molding services, including mold design services. We serve a wide range of industries requiring mission-critical parts.

Our in-house Master Molders are technically trained and formally certified in plastic mold design, analysis, troubleshooting and resolution relating to complex molding projects.

Contact PMC for design assistance, or send us files to get a quote; we’ll respond shortly!