Everything You Need to Know about Plastic Trim Molding

Jan 29, 2021


Plastic trim molding is the most common and modern production method for mass manufacturing of plastic products. These products are being used in a variety of industries and applications. It is, perhaps, most beneficial when you use it to develop large quantities of the same product.


When we look into the history of plastic trim molding, we see how it was actually invented to solve an issue for billiards. In the nineteenth century, billiard balls were made up of ivory harvested from the tusks of African elephants.

Everything You Need to Know about Plastic Trim Molding

This devastated the elephant population, so a billiards manufacturer offered a ten-thousand-dollar prize (3 million dollars in today’s time) for a replacement for ivory.

This led Wesley Hyatt to develop one of the earliest plastics - celluloid - to make billiard balls. He patented an apparatus for molding products plastics from celluloid. This apparatus was the birth of injection molding.

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The technology is used to create many products we use everyday; ranging from a toothbrush to the handle of a pressure cooker and from a toy to medical equipment.

Other examples include doors, decorative household items, window cases, ceilings, bottle caps, chairs, cases for consumer electronics, automotive parts, disposable cutlery, pocket combs, small tables, containers, lego bricks and many more. So, the products obtained by this method range from simple to complex.


In principle, plastic trim molding is simple: First the plastic raw material is melted and injected into a mold. It is allowed to cool down for a while after which the plastic product is ready.

A large product often requires a large machine with high pressure and large mould. Whereas, for a smaller product, a low pressure machine and small mould are sufficient. A mitre box then comes into action to trim the molding into the desired shape.

You place the molding inside the box upside down and at a certain angle. Then use clamps to fasten the molding in the box.  You mark the mitre box  with different angles.

Place the saw at a 45 degrees angle and start sawing. This is how any desired shape and size is achieved through plastic trim molding. In reality, however, plastic trim molding is a very intricate and sophisticated process.


You can use a variety of materials for trim molding.. Here we compare the two most widely used materials PVC and wood.


It is common knowledge that plastic trim molding is useful for manufacturing PVC pipes. People use them universally for plumbing drains. These days this technique produces far more versatile products. Over the years, PVC has become extremely popular.

In general, the words trim and casings refer to the pieces of linear lumber that cover the border corners and edges of our homes. For many years, manufacturers use wood and its respective prodcutss to create trim.. However,t the problem was that wood trim really struggled in wet locations.

 It can get saturated in certain places because it is organic and can rot. Therefore, the construction industry wanted a material that was truly impervious to rot and water penetration. This led them to invent cellular PVC.

The most important differences between wood and PVC that manufacturers use  for trim molding are chemical in nature. Wood swells up in the presence of moisture and PVC expands due to heat.

In winter, it shrinks and in summer, due to rising temperature, expands. However, unlike wood trims, the PVC trims do not warp due to environmental factors making it the superior choice.


We can install PVC trim virtually anywhere in the world today, typically in the doors and window section. Comparing it to the wood trim, the PVC trims are relatively expensive.

You can use PVC trims for any part of the house exposed to moisture. This includes virtually every trim component on the exterior of the house. The important candidates for PVC trims are window sills, brick molds around doors and windows in fascia boards.

Certain rooms inside the house are also great places to install PVC trims, especially the bathrooms. PVC is very convenient to work with and you can cut it almost as easily as wood. Moreover, PVC is actually easier to jigsaw because there is no grain to resist the blade.


Different enterprises have specialized in various techniques for producing plastic trim components of desired quality. There are a variety of processes available in the market and hence the consumer can choose what he desires. Below are some of these processes.


To ensure the strength of the quality, you can use compression molding. The products are easily moldable. The typical products of this process include the rugs, fiberglass composites,  fascia boards etc.


In twin sheet molding, manufacturer use the principles of compression molding, vacuum molding and blow molding collectively. So using this process we can mold, laminate and trim various layers of a material at the same time.


The classic products of vacuum molding are door bolsters and seatbacks . It binds the sheet materials like vinyl and soft touch plastics into injection molded parts.


In plastic thermoforming as the name suggests produces single sheet products via heating them. This technique uses the negative air pressure for this purpose. Manufacturers use plastic thermoforming for water shields and consumer packaging.  


  • One of the biggest advantages of plastic trim molding is that we can create large volumes of product at high speed. This is difficult to do with metal and wooden products.
  • In addition, we can create almost any shape we desire. Today there are many different plastics to choose from. We can create the form and function of our product exactly like we want it thanks to injection molding.
  • Plastic trim molding is relatively cheap owing to its efficiency and speed.
  • Another upside to this process is how expandable it is. Every country and every state has it, so you can make your products anywhere you want in the world.
  • There is a lot of plastic waste floating around in our oceans that can be recycled into new products through injection molding.
  • All the samples of the desired product are exactly similar giving them a more professional look.
  • Trim molding also offers design flexibility and use of multiple materials.


  • A drawback of plastic trim molding is restriction in terms of part design.
  • The small run of plastic trim molding is very costly because one of the expensive parts of the machine is the mold and one mold is only good for one type of product.

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 John Wesely Hyatt and his injection molded billiard ball did not win the ten thousand dollar prize - his celluloid billiard balls did not bounce quite right - but he did pioneer molding, a thriving, continually evolving manufacturing process which creates many billions of products every year.

Manufacturers have been using plastic trim in a variety of settings from basic consumer products to building and construction. Although this process has its limitations, but if we compare the advantages and the disadvantages, it becomes quite clear that it is always advisable to use plastic trim molding for manufacturing plastic products.

In today’s era, good quality molded products are in high demand. This method provides a cost effective and efficient way of meeting this demand. It has been providing us such valuable trimmed and molded articles for over a hundred years now. In addition, the only way to avoid the hazardous effects of plastic build up in our oceans is to recycle it by plastic trim molding.

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Everything You Need to Know about Plastic Trim Molding