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Vetting Checklist for Custom Injection Molders

The Polysort plastics and rubber industry directory contains an extensive list of custom plastic injection molders, providing descriptions and links to the various company websites. But short descriptions can only take you so far. What else do you need to know to select the right supplier for your project?

While cost is an important consideration, it shouldn’t be the sole driver of your decision. One basic differentiating factor among injection molders is volume. Low to moderate volume plastic molders specialize in the production of parts numbering under 10,000 units, while high volume molders are chosen for jobs running over 750,000 units.  Knowing the volume of production you need will help steer you toward the right molding company.

Here’s a list of other questions to ask as you vet the custom injection molders you find.

General Considerations

What is their main area of expertise? It only makes sense to select a molder that specializes in your product.

What obstacles have they encountered and how have they overcome them?

Is quality a priority – are they ISO certified and compliant? This is a requirement for most automotive suppliers, but an emphasis on quality can benefit any end product.

Is everyone, from engineering and design through production and shipment educated about each customer’s expectations and deadlines? Communication is a key to ensuring you get the product you want when you want it.


Is design and tooling assistance provided? Most of the time and money savings are generated during the design phase of a project. It’s important to find custom injection molders that can get in on the ground floor and help you achieve all possible cost reductions and efficiencies.


How many shifts do they run – do they have the production capacity to meet your needs?

Do they have the capability to mold complex geometries and variations in wall thickness? If you have a complicated part to produce, you’ll want to make sure the molding company has mastered these tricky areas.

What are the size parameters – how big or how small can they mold, both in terms of physical dimensions and weight?

Is there an emphasis on cleanliness on the factory floor? Will the molder be able to avoid contamination of your product?


Do they have the expertise necessary to make material recommendations to achieve your performance requirements?

Do they offer a range of materials to meet your needs?

Are they educated about the processing requirements of your preferred material? Do they understand the mechanical properties that your product requires? One processing misstep can ruin an entire production run.


Are inspection services provided? In-house testing can provide the peace of mind you need.

Are secondary services, like packaging and warehousing, available? Finding a one-stop shop can save you time and money.

A good website will provide a lot of this information, but there’s nothing like in-person experience during the vetting process. Many custom plastic injection molders welcome plant visits – make sure to ask if you can have a tour and see their production process for yourself.

Get your vetting process started today – visit to see our complete list of injection molders.


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