Table of Contents

1. What Is Thermoforming?

2. What Is Thermoforming? 2.1 How Thermoforming Works? 2.2 Advantages of Thermoforming 2.3 Limitations of Thermoforming

3. What Is Injection Molding? 3.1 How Injection Molding Works? 3.2 Advantages of Injection Molding 3.3 Limitations of Injection Molding

4. Key Differences: Thermoforming vs Injection Molding

5. Real Case: Why Judging the Process Isn’t Always

6. Selection Guide of Thermoforming vs Injection Molding

7. Conclusion

1. Introduction

In the plastics manufacturing world, thermoforming and injection molding are two processes that customers frequently compare. When clients send us product drawings or photos, the first question we often hear is:

“Should this be made by thermoforming or injection molding?”

It sounds simple, but in real engineering projects, the answer is often far from obvious. In automotive interiors, medical equipment housings, industrial trays, electronic enclosures, and many other projects we've handled, we’ve seen countless situations where:

Choosing the wrong process → mold cost skyrockets → mass production is delayed → structure becomes unachievable → redesign or even remolding becomes necessary.

This article isn’t about repeating textbook definitions. Instead, it’s based on real engineering experience inside our factory—how we actually evaluate processes, how we avoid unnecessary iterations, and why some products look like thermoformed parts but actually need injection molding.

We’ll also share a very typical case from a recent Turkish client, which perfectly illustrates an important point:

You can’t judge a manufacturing process by appearance alone. You must consider the product’s purpose, quantity, structure, and cost as a whole.

2. What Is Thermoforming?

Thermoforming works by heating a plastic sheet until soft, then using vacuum or air pressure to pull it over a mold surface. After cooling, the formed shape is trimmed to the final outline.

In simple terms, it “shapes a plastic sheet” and is ideal for large, simple enclosures or trays.

2.1 How Thermoforming Works

• Plastic sheet is heated

• Sheet softens and drapes over the mold

• Vacuum or pressure forms the shape

• Part cools and retains shape

• Excess material is trimmed

• Optional secondary operations if needed

2.2 Advantages of Thermoforming

• Very low mold cost

• Fast development (samples in 7–10 days)

• Excellent for large housings, trays, covers

• Design changes are inexpensive and flexible

2.3 Limitations of Thermoforming

• Loose dimensional tolerance

• Complex internal structures cannot be formed

• Thickness distribution may be uneven in deep zones

• Requires an additional trimming process

• Thermoforming is widely used for industrial trays, automotive interior panels, displays, and large covers.

3. What Is Injection Molding?

Injection molding is completely different:
Pellets melt → material is injected under high pressure → mold cools → automatic ejection → cycle repeats.

It is the go-to process for complex geometries, strong parts, tight tolerances, and large-volume production.

3.1 How Injection Molding Works

• Plastic pellets melt in the barrel

• Molten resin is injected into the mold

• Resin cools and solidifies

• Mold opens

• Ejector system pushes the part out

3.2 Advantages of Injection Molding

• Extremely high dimensional accuracy

• Excellent surface quality (texture, gloss, matte, mirror finish)

• Suitable for complex functional structures

• High-volume production with stable consistency

• Strong mechanical properties

3.3 Limitations of Injection Molding

• High mold cost (steel tooling, cooling systems, sliders, ejectors)

• Design changes are costly

• Not suitable for small quantities

4. Key Differences: Thermoforming vs Injection Molding

Below is a comparison based on real project experience, not theory.

Comparison Dimension	Injection Molding	Thermoforming
Molding Principle	Heat and melt plastic pellets, then inject them into a closed mold cavity at high pressure. The product is obtained after cooling and solidification followed by demolding.	Heat and soften plastic sheets, then adhere them to the mold surface via vacuum negative pressure adsorption. The product is completed after cooling and trimming.
Mold Condition	Mostly precision steel molds, which can be designed with complex textures, multiple buckles and holes. High mold cost (single set up to 28,220 - 42,330 US dollars) and long development cycle (about 2 months).	Mostly ordinary aluminum molds, only suitable for simple line designs. Low mold cost (single set from about 141 to 2,822 US dollars) and short development cycle (about 20 days).
Product Characteristics	Uniform product thickness (tolerance controllable within ±0.1mm), stable structure. Capable of integral molding of special - shaped and complex three - dimensional parts with high dimensional accuracy, good resilience and durability.	Thickness unevenness due to stretching (thinner at stretched areas like cup bodies). Mostly thin - walled shell parts with simple structure, poor recoverability and low dimensional accuracy.
Material Requirements & Adaptability	High requirements for material fluidity and melting performance. Wide range of adaptable materials, such as PP, PE, polycarbonate and other plastic pellets.	Adaptable materials are mostly thermoplastic sheets (e.g., PP, PET), often mixed with blends. Relatively limited material options.
Production Efficiency	High degree of automation, suitable for continuous mass production. Short single - mold cycle; labor costs are amortized in mass production. For 1 million cups, the unit cost is 0.014 - 0.028 US dollars lower than thermoforming.	Requires sheet - by - sheet heating and molding, plus additional trimming processes. Low production efficiency and high labor dependency. High proportion of labor cost per unit, suitable for small - batch production.
Equipment Investment	Requires large high - pressure injection molding machines and other equipment, some equipped with robotic arms for part removal. High initial equipment investment.	No need for large high - pressure equipment; the equipment structure is relatively simple. Low initial investment.
Typical Application Scenarios	Auto parts, home appliance casings, special - shaped milk tea cups, gears, electronic product housings, wire and cable sheaths, etc.	Food trays, cold milk tea cups, display covers, packaging boxes, trunk mats, simple display racks, etc.

5. Real Case: Why Judging the Process Isn’t Always Straightforward (Turkish Customer Example)

Not long ago, we received several product photos from a Turkish customer. They showed a tray-type part—large surface, simple cavity shapes, evenly rounded corners.

At first glance, it looked exactly like a thermoformed product.

• Large panel
  Simple cavity structure
  Uniform depth
  No visible undercuts

Naturally, our engineers initially assumed it was thermoformed.

Later, the customer sent a close-up photo of the back side.
Surprisingly, we saw:

A series of evenly spaced circular marks—just like ejector pin marks.

This detail immediately told us:

This part was actually injection molded.

The customer was surprised too; he assumed it was a thermoformed tray.

However, after discussing his real usage, we learned:

The required quantity was not high

The product only needed to store tools

Precision and strength were not critical

We provided two options:

Injection molding: Stronger, nicer appearance, but expensive tooling

Thermoforming: Much cheaper, faster, and fully sufficient for his application

In the end, the customer chose thermoforming—it delivered the best value for his needs.

This case highlights an important truth:

Choosing the correct process is never about “what it looks like,” but “what the product truly requires.”

6. Selection Guide of Thermoforming vs Injection Molding

Here is a practical engineering-based framework our team uses to quickly determine the correct manufacturing process.

Choose Thermoforming If:

Product is large

Structure is simple

Tolerance is moderate

Quantity is 50–10,000 pcs

Fast development is needed

Budget is limited

Design is likely to change

Typical products: trays, covers, panels, interior parts, display trays.

Choose Injection Molding If:

Product has complex structures (ribs, bosses, snap-fits)

High precision is required

Strength matters

Surface finish matters

Volume is high (tens of thousands to millions)

Product requires long-term consistency

Typical products: electronic housings, medical components, engineered internal parts, consumer products.

7. Conclusion

At this stage, if you are evaluating which manufacturing method fits your project best, our engineers at Alpine Mold can review your drawings, expected annual usage, and performance requirements, and provide a professional recommendation with cost comparisons.

As a specialized injection molding and mold manufacturing company with over 20 years of experience, Alpine Mold supports:

Mold design and engineering optimization

Prototype validation

Precision steel/aluminum mold manufacturing

Mass production with strict quality control

Material selection guidance

Assembly and secondary processing

Whether you already have a final CAD design or only an initial concept, we can help move your project into stable production efficiently.