If you’re looking to become a plastic molder, the two main things you should consider are your plastic injection molds and the materials you’ll use to create parts. Before setting out to have your mold designed and made by Quality Mold Shop, you should consider the purpose of the part you plan to create.

Choosing the Right Plastic for the Right Job

Different plastics have different properties, making some more suitable for certain jobs than others. If you take a look around you, noticing different things made from plastic, you’ll notice how similar plastics are always used to make similar products.

Your laptop case, for instance, will always be made from a hard plastic rather than a soft one. If you examine the properties of the plastic used to make laptop cases, you’ll notice that the plastic doesn’t really give way or bend easily. It’s hard, yet it’s durable enough to not break or crack easily if it gets a light knock. The lid on your lunch box, on the other hand, isn’t hard like that. It’s a soft plastic that easily bends and gives way. This can help it to stretch a little over the lunch box container, creating a stronger seal.

If you used a hard plastic to make a lunch box lid, it wouldn’t stay on the container as securely. And if you used a soft, bendable plastic to make a laptop case, it wouldn’t protect the hardware inside the computer from light knocks.

In both cases the plastic used was picked carefully based on the function of the part that’s being made. This is what makes plastic such a popular material for manufacturing, its versatile. But that versatility comes in the form of different polymers. After looking into plastic injection molding and different types of plastics available, you’ll see that laptop cases are most often made of plastics like ABS (acrylonitrile butadiene styrene), while lunch box lids are made from materials like polyethylene.

Practical Considerations

Of course the ultimate function of a molded plastic part will be an important consideration when choosing the right polymer for the job. But how will you know what factors to consider in order to choose a plastic with the right properties?

Here are some of the practical things to consider when choosing what material to use for your plastic parts.


Some polymers are just more expensive than others, so the market value of your final product will have a big impact on your choice of polymer. The raw material could cost you anywhere from less than a dollar per pound, to as much as $50 dollars if you need a specialty material. So obviously the possible price fluctuation is huge.

And it goes without saying that you simply can’t use a polymer that costs $50 per pound as a raw material, if your final product will requires a pound, but will only cost $40. That’s an oversimplified example, but it drives home the point that cost is vitally important when choosing what plastic to use.


Some products don’t need to be very durable at all, while other products are expected to last as long as a lifetime. You’ll know how durable you expect your product to be before having a mold made, and so you should choose a plastic that can live up to these expectations.

People don’t expect disposable plastic cutlery to be particularly durable, but a reusable plastic cup should be made of plastic that won’t easily crack like its disposable counterpart.

Another essential part of choosing a durable material is its resistance to temperature. A simple plastic like polyethylene isn’t very temperature resistant. So while it’s a good plastic for everyday objects, it won’t perform well under somewhat more extreme temperatures. While hot conditions isn’t good for the material, cold conditions also negatively affect its plasticity. Meaning that a part made from polyethylene can actually break or shatter below freezing point, losing its ability to flex.

Part Design

The shape of the part you want to make will influence the polymer you choose. Simple shapes can be made using almost any polymer, but if the part you want to mold will have more holes, depressions, ribs and gussets, you have to pick your polymer more carefully. Not all plastics can be as easily shaped as others.

And while aesthetics isn’t necessarily the most important thing to consider, it’s also something that will influence your decision. Getting a plastic with high gloss, or one that will be good for making a part with a matt effect might be important to you.


Some parts are meant to be able to bend a lot without cracking, while others are made not to bend. It goes without saying that any part that will have to flex a lot, should be made from a plastic that can handle this kind of tension without snapping and breaking. But some parts are meant to stay securely in place under pressure without flexing or giving way, and these parts should be made from harder, yet durable plastics.

The best way to know what plastics will be a good fit for your project is to talk to professionals. Follow the advice from both the engineers working to make your molds, and a chemical engineer. After all, the best way to get it right the first time is to not base your choices on guessing games, but to rely on sound professional advice.

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