Thermoforming Mold Basics: How Thermoforming Molds Work, Types, and Key Design Considerations (Part 1)

When factories, packaging suppliers, or brand owners start exploring thermoforming for the first time, one of the most common questions is: “How do thermoforming molds actually work?”

This introductory guide provides a beginner-friendly explanation of thermoforming mold basics—types, examples, and key concepts—so that new buyers can understand the fundamentals before moving on to advanced engineering topics such as venting, cooling design, cycle-time optimization, and mold durability.

Looking for a full engineering-level guide? See our flagship article: Thermoforming Mold Guide: Design, Materials, and High-Performance Tooling for Food Packaging.

1. How does a thermoforming mold work?

   
   

   Thermoforming has different processes. And how the mold works is different in these processes. Though, there are many processes, but we'll go with the most commonly used processes to explain how thermoforming mold works. These processes are:

   • Vacuum Forming:

     The process uses air created by the vacuum. A two-dimensional thermoplastic sheet is heated to a forming temperature. The mold is already designed in the desired shape or form. The heated plastic is then placed directly on the mold. The air in the mold will be evacuated from the mold which will pull down the heated plastic to sit inside the mold. This will make the plastic assume the shape or form of the mold. After cooling, the desired part is then removed and trimmed to specifications.

     
     

     

   • Pressure Forming:

     This process is similar to the vacuum forming process. But there's an extra step. In this process, the heated plastic material is pulled into the mold just like the vacuum. A pressing tool is then used to apply more pressure on the plastic in the mold to exact its definite shape or form.

   
   

   In general, a thermoforming mold is designed in different shapes and forms to collect the heated thermoplastic sheet, and give it form or shape as designed or required.

   
   

   Read also: 5 Minutes to Understand Vacuum Thermoforming : Mold Design & Examples

   
   

   

   
   

   

2. Common Thermoforming Mold Types (Forming vs. Trimming)

   
   

   Thermoforming uses more than one type of mold depending on the stage of production:

   • Forming Mold:

     Shapes the heated sheet into its basic geometry
     Typically made of aluminum or steel
     Designed with cavities, vents, and sometimes plug-assist systems

   • Trimming Mold:

     Cuts the formed part into its final outline
     Ensures the accuracy of rims, edges, and fit
     Often includes holes, pins, and locating features for precision cutting

   
   

   Forming = create the shape
   Trimming = finish the shape

   
   

   

3. Examples of Thermoforming Mold Applications

   
   

   Thermoforming molds are used across consumer, industrial, and food sectors:

   • takeaway containers
   • pastry boxes and cake domes
   • fruit and vegetable trays
   • clam-shell blister packs
   • dairy cups and lids
   • medical blister packaging

   
   

   For more thermoforming mold examples: Mold Introduction

   You may be also interested in: Thermoforming Cup Mold Design.  ｜  Clamshell Packaging Design.

   
   

   

   
   

   

4. The Basic Workflow of Creating a Custom Thermoforming Mold

   
   

   For buyers who are new to mold procurement, the typical workflow looks like this:

   • Define requirements

     Product size, shape, stack height, sealing needs, and material type (PET, PP, PS, PLA, etc.)

   • Choose mold material

     Aluminum for precision
     Steel for durability
     Hybrid structures for cost-efficiency

   • Create prototype

     Physical samples or 3D-printed models to validate shape, dimensions, and packability.

   • Engineering refinement

     Add vents, plug assist shapes, and cooling considerations.

   • Final mold build

     CNC machining, polishing, finishing, assembly, and testing.

   
   

   Read also: Choosing the Right Cutting Dies and Tools for Thermoforming Machine

   
   

   

5. Introductory Design Considerations for Beginners

   
   

   Before you move to engineering details, these basic factors should be understood:

   • Production volume

     : molds for high-speed food packaging must withstand continuous operation.

   • Material type

     : PET, PP, PLA, and PS behave differently under heat and forming pressure.

   • Cooling performance

     : cooling channels and venting strongly affect cycle time and part consistency.

   • Forming forces

     : vacuum, pressure, or mechanical assist must match the desired part geometry.

   
   

   Read also: Design considerations for thermoforming food packaging

   
   

   Click here to read more about Thermoforming Mold Advanced Guide: Cost, Packaging Innovations & Selecting the Right Manufacturer (Part 2)

Building a Solid Understanding Before Moving Forward

Thermoforming molds may appear simple on the surface, but the principles behind forming methods, mold types, airflow, shrinkage, and basic design considerations form the foundation of every successful thermoforming project. By understanding how vacuum forming, pressure forming, and plug-assist systems behave—and how forming and trimming molds function together—manufacturers can avoid common early-stage mistakes and make more informed decisions when developing new packaging.

If you are ready to go deeper into thermoforming mold engineering, including cost drivers, advanced packaging design options, and how to evaluate the right mold supplier, continue with Part 2 of this series.

For a complete, engineering-level overview of thermoforming mold design, cooling systems, venting strategy, and food-packaging applications, explore our in-depth guide: Thermoforming Mold Guide: Design, Materials, and High-Performance Tooling for Food Packaging.

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