Thermoforming

Thermoforming shapes heated plastic sheet over molds to create thin-walled shells with low tooling cost, ideal for medium to large parts at scale.

Overview

Thermoforming heats a plastic sheet until pliable, then forms it over a mold using vacuum, pressure, or two opposing tools. Once cooled, the formed part is trimmed to final shape. It excels at producing thin-walled, relatively large plastic parts with modest tooling costs and fast cycle times. Expect good cosmetic surfaces and functional accuracy, but not injection-molding-level tolerances.

Vacuum forming pulls the sheet onto the mold with vacuum for economical parts and simple to moderate detail. Pressure forming adds positive air pressure for sharper features, tighter radii, and better textures. Twin sheet forming clamps and forms two sheets together to create hollow, double-walled structures with internal cavities. Thermoforming fits best when you need lightweight covers, panels, and enclosures in low to very high volumes, but can accept some wall thickness variation and forming-related draft and radii limits.

Common Materials

  • ABS
  • HIPS
  • PETG
  • Polycarbonate
  • HDPE
  • Polypropylene

Tolerances

±0.010" to ±0.030" on formed features, looser on large overall dimensions

Applications

  • Equipment and machine covers
  • Automotive interior and exterior panels
  • Appliance and HVAC housings
  • Medical device enclosures and carts
  • Custom trays and inserts for packaging
  • Point-of-purchase and display components

When to Choose Thermoforming

Choose thermoforming for thin-walled plastic shells, panels, and enclosures where you want relatively low tooling cost, good cosmetics, and moderate dimensional precision. It suits medium to large part sizes, low to very high production volumes, and designs that accept draft, radius constraints, and some wall thickness variation. It is especially effective when you can design around single-sided tooling and consistent draw directions.

vs Injection molding

Pick thermoforming when you need large, relatively thin plastic parts but want to avoid very high steel tooling costs and long mold lead times. It is better suited to panels, covers, and enclosures where wall thickness can vary and you can live with looser tolerances and single-sided detail.

vs CNC machining

Choose thermoforming over CNC machining when producing repeated plastic housings, covers, or trays where material removal would be slow and wasteful. Thermoforming amortizes mold cost across volume and gives faster cycle times and better per-part economics for production quantities beyond small prototype runs.

vs 3D printing

Select thermoforming instead of 3D printing for production-scale quantities and larger parts where you need better unit cost, consistent surface finish, and stable material properties. Use 3D printing for early form-and-fit prototypes, then move to thermoforming once the design stabilizes and you need repeatable, economical parts.

vs Blow molding

Use thermoforming when you need open-backed shells, trays, or panels rather than fully closed bottles or tanks. Twin sheet forming can compete with blow molding for hollow, structural parts, especially when you want more control over outer aesthetics, flat flanges, or integrated mounting features.

vs Sheet metal fabrication

Choose thermoforming over sheet metal when weight reduction, corrosion resistance, and complex 3D curvature or textures are more important than very high stiffness and temperature capability. Thermoforming can integrate ribs, bosses, and aesthetics in a single part where metal might require multiple operations and assemblies.

Design Considerations

  • Design with adequate draft (typically 3–5° or more) on draw surfaces to allow reliable forming and easy part release
  • Maintain as uniform a wall thickness as possible and respect practical draw ratios to avoid thinning, webbing, and tearing
  • Use generous inside radii and avoid sharp corners to promote material flow and reduce stress concentrations and cracking
  • Place critical cosmetic surfaces against the mold side that gives the best finish (female vs male tool) and define surface texture requirements clearly
  • Define trim lines, hole locations, and datums explicitly so the shop can design accurate trim fixtures and quote secondary operations correctly
  • Minimize undercuts and deep reverse features unless you are prepared for more complex tooling such as plug assists, inserts, or moving sections