Thermoforming

Thermoforming shapes heated plastic sheet over a mold for fast, cost-effective large-area parts with moderate detail, best at prototype to production volumes.

Overview

Thermoforming heats a thermoplastic sheet until pliable, then forms it over a mold and trims the finished part. It excels at lightweight, large-surface-area components where you want low tooling cost and quick turnaround versus hard tooling processes.

Choose thermoforming for prototypes through medium/high volumes when part geometry is mostly single-sided with controlled draft, smooth radii, and features that can tolerate thickness variation. Typical tradeoffs are looser tolerances than machining, wall thinning in deep draws, and secondary ops (trim, drill, insert, weld) to finish edges and add attachment points.

Common sub-processes include vacuum forming (economical, good for larger/simple shapes), pressure forming (better detail and sharper features), and twin sheet forming (forms two shells and fuses them for hollow, stiff structures and internal air/flow cavities).

Common Materials

  • ABS
  • HIPS
  • Polycarbonate
  • PETG
  • HDPE
  • Acrylic

Tolerances

±0.020" to ±0.060" (trimmed features often tighter with fixturing)

Applications

  • Equipment housings and covers
  • Medical device trays and packaging
  • Vehicle interior panels and liners
  • Appliance panels and door liners
  • Material handling dunnage and trays
  • Kiosks and signage enclosures

When to Choose Thermoforming

Thermoforming fits parts with a dominant show surface, large footprint, and moderate feature detail where sheet-based forming keeps tooling and piece price low. It works well when you can design for draft and accept some thickness variation across deep draws. It’s a strong choice when you need quick prototype iterations that can scale into production with the same process family.

vs Injection molding

Choose thermoforming when part size is large, volumes are moderate, or you need lower-cost tooling and faster lead times. It’s well-suited to shallow-to-moderate depth shapes and cosmetic outer skins, even if you’ll add inserts or secondary assemblies after forming.

vs CNC machining

Choose thermoforming when the part is primarily a thin-wall shell or cover and machining would waste material and time. It’s often more economical for large contours and smooth surfaces, with machining reserved for trimmed edges, holes, and fixture-critical features.

vs 3D printing (polymer)

Choose thermoforming when you need repeatable production parts with better surface finish options and lower piece cost at volume. It’s also a practical path when you can build a mold (or printed tool) quickly, then run consistent parts without long print times.

vs Fiberglass/FRP layup

Choose thermoforming when you want cleaner, repeatable plastic parts with shorter cycle times and less manual labor. It’s a better fit for thinner, lighter shells and for programs needing consistent cosmetic surfaces and predictable lead time.

vs Rotational molding

Choose thermoforming when the part is an open shell or two-piece assembly rather than a fully closed hollow body. It typically gives faster cycles and better definition on one cosmetic face, with more control over local detail via pressure forming.

Design Considerations

  • Add draft on all formed walls (typically 3°+; more for deep draws and textured surfaces)
  • Use generous radii and avoid sharp corners to reduce webbing and thinning
  • Control draw ratio and depth; expect wall thinning in deep areas and design thickness-critical zones near the flange when possible
  • Define trim lines clearly and allow a trimming flange for fixturing and repeatable edge accuracy
  • Avoid undercuts unless you plan for slides, multi-piece tooling, or secondary assembly operations
  • Call out cosmetic “A” surface and texture requirements; specify where witness marks, vents, or clamps are acceptable