What is Plastic Molding?

Plastic molding (sometimes spelled “moulding” depending on where you live) is the highly effective process of manufacturing a custom plastic part by shaping liquid or pliable material using a rigid mold or frame.

While the molding process has been around since the late 1800s, the technology has come a long way since its inception. Recent process enhancements, better equipment, automated technology and improvements in material have helped ramp up the popularity of using molding to create finished plastic products and parts in a cost-effective way at scale.

But this widespread adoption isn’t without challenges and obstacles.

The ability to produce high performing plastics using various molding techniques is both an art and a science. When mass-producing plastic parts, extensive technical knowledge, competent expertise and great attention to detail are all needed to ensure small errors don’t end up costing companies big bucks.

In short, finding the right team of people with relevant expertise is the most important part of the process


Why Hire Our Plastic Experts?


Dr. Duane Priddy and his team of plastic experts specialize in the art and science of plastic molding analysis and design. Dr. Priddy is considered to be one of the world’s leading experts on plastic technologies and he was recently interviewed by CBS News’ 60 Minutes about a national gynecological polypropylene mesh investigation.

Our team of consultants are world-renowned scientists and authors, as evidenced collectively by the more than 500 scientific papers, 100 US patents, many books, and encyclopedia articles on plastics we’ve authored. In addition, our team has specific expertise in injection molding process optimization and blow molding, as well as proven experience on how to troubleshoot injection molding processes.

Our Clients

Trusted by nationally recognized industry leaders

Our Customer Reviews

Putting the needs of our customers first as evidenced by our client testimonials

One of my company’s most well-established products failed during use and we were being threatened with a possible litigation. Dr. Priddy proved that our product was not defective. I plan to continue to use Plastic Failure Labs to solve all of my polymer analysis, plastic consulting, and plastic failure analysis needs.
— Frank Webb, Paragon Sourcing
Dr. Duane Priddy’s failure investigation clearly identified the defects in the product that injured my client. His expert opinion report was meticulously prepared and his conclusions supported with excellent data and bases. I plan to continue to use Plastic Failure Lab for my cases involving defective plastic parts.
— Tony Baratta, Baratta Russel Baratta

Common Plastic Molding Defects:
Troubleshooting Problems & Solutions

Industry data and our own experience tells us that plastic molding defects can usually be traced back to one of four parameters in the molding process:

  • Machines. A majority of plastic defects are caused by faulty production tools such as a malfunctioning or misused molding machine, screw or heating cylinder.

  • Mold. A poorly designed mold from the start can result in a wide range of defects later on.

  • Material. Inferior plastic material can make defects more likely.

  • Men. A mistake by the molding machine operator (human error) or in how the manufacturer maintains and stores the material prior to production can lead to defects.


The most common quality defects associated with inferior plastic molding include:

  • Flow lines - A common plastic injection molding defect in which discolored ring-shaped streaks, patterns, or wavy lines appear around gates or narrow sections of the finished product.

  • Burn marks - Often appears as black or rust-toned discoloration streaks on the edge or surface of a molded product.

  • Warping - The structural deformation that occurs due to uneven shrinkage in various parts of the plastic product.

  • Air pockets - Vacuum voids (the presence of holes) and pockets of air can get trapped inside the molded product.

  • Sink marks - Small potholes or depressions in the otherwise flat surface of a product which occur when inner parts of a molded component shrink, collapsing material from the outside inward; more common in thicker areas or materials.

  • Weld lines - A hair-like line on the surface where material splits in two and flows in different directions; reduces product strength and integrity.

  • Jetting - A visible squiggly line that appears on the surface of the finished part (typically leading from the initial gate of injection) that is caused when an initial “jet” of molten material is injected into the mold cavity that starts to solidify before the cavity is filled.

  • Nonfill (“short shots” or “short mold”) - An incomplete mold that isn’t fully filled, leading to deformation or “shortened” parts; can be caused by blockage, bottlenecking or injection that is either too fast or too slow.

  • Flash (“burrs” or “spew”) - An excess of material that appears as a thin lip or extrusion defect at the edge of a plastic mold; it cools and remains attached to the finished product.

  • Blistering - A raised area on the plastic surface, generally caused by too much heat on the tool or by inadequate cooling or venting.

  • Contamination - Embedded contaminates mean that somehow foreign matter has found its way into the resin material and must be cleaned.

  • Splaying (“silver streak” or “black specks”) - A condition when streaks of a silvery white color or black specks appear in the material flow direction.

  • Discoloration (color streaking) - When a molded part is a different color than desired.

  • Surface delamination - A molding defect where thin surface layers appear on the part and can easily be peeled off.

If not addressed properly and swiftly, minor product defects can quickly become a major and costly liability for the manufacturer — ultimately hurting your bottom line.

Regardless of which type of plastic molding technique you use — rotational molding, injection molding, blow molding, compression molding, extrusion molding or thermoforming — it’s important to plan accordingly and address problems as they arise immediately.

Don’t Let a Plastic Parts Defect Pinch Your Profits

Our plastic consultants can help you discover the best process to make your part or product. If you’ve already discovered a plastic molding defect, we will root out the source of the problem and recommend the best countermeasures and solutions to remedy the issue.

We perform Finite Element Stress Analysis (FEA), failure analysis and injection mold-flow design calculations on your part to ensure that the material and design will be able to withstand the rigors of the intended use of your product at the lowest possible cost of manufacture. Plus, when failure of a plastic part occurs, our experts can explain what went wrong and determine the best solution.

Need a plastic expert? Contact us to obtain a quote for our forensic failure analysis services or tell us about your problem.

Case Studies

Continue reading our case studies to find out how we helped businesses like yours solve their plastic defect problems.