The complete guide
What is thermoforming?
Thermoforming is a plastic manufacturing process in which a thermoplastic sheet is heated to a pliable forming temperature, shaped over a mould using vacuum and/or air pressure, cooled to set, and trimmed to a finished part. It spans everything from high-speed food packaging to large structural covers — and, because tooling is fast and inexpensive, it is often the most cost-effective way to make large or low-to-medium-volume plastic parts. This guide explains how it works, the main types, the materials, how it compares with injection moulding, and where it is used.
How thermoforming works — step by step
At its core, thermoforming is four moves — heat a sheet, form it to a tool, cool it, then trim it. Here is the full cycle at a glance:
On the production floor those four moves become six controlled stages — we clamp and load the sheet before heating, and add a pre-stretch step for even walls on deep draws. Getting each one right is what separates a consistent, dimensionally stable part from a warped or thin-walled one:
Clamp & load
A thermoplastic sheet (or roll) is clamped into a frame over the mould. Sheet gauge is chosen for the part — 0.1–2 mm for thin gauge, up to 12 mm for thick gauge.
The right sheet for the part
Heat
The sheet is heated by zoned infrared or convection heaters to its forming temperature (typically ~120–200 °C depending on polymer), with sag sensors keeping it uniform.
Uniform heat, consistent forming
Pre-stretch
For deeper or more uniform parts the softened sheet is pre-stretched — billowed with air and/or pushed by a plug assist — so material is distributed before it touches the tool.
Even walls on deep draws
Form
Vacuum (and/or air pressure) draws the sheet tightly onto the mould, reproducing its shape and surface. This is the moment that defines detail, radii and wall distribution.
Detail, radii & distribution set here
Cool & set
The formed part is cooled — by air, and by temperature-controlled tooling where tight tolerances demand it — until it holds its shape dimensionally.
Dimensional stability locked in
Trim & finish
The part is released and trimmed to net shape, at Indu on 5-axis CNC routers against part datums, then drilled, decorated, assembled and inspected as required.
Clean edges, ready to assemble
The main types of thermoforming
"Thermoforming" is an umbrella term. The methods below differ in how hard the sheet is pushed into the tool — which decides surface detail, depth of draw and cost.
Vacuum forming
The workhorse method: atmospheric pressure pushes the heated sheet onto the tool as a vacuum evacuates the cavity. Economical, fast, ideal for covers, trays, liners and panels.
Pressure forming
Adds compressed air (2–4 bar) behind the sheet for 3–5× the forming force — giving crisp radii, sharp textures and embossed detail approaching an injection-moulded finish, for a modest tooling premium.
Plug-assist forming
A shaped plug mechanically pre-stretches the sheet into deep cavities before vacuum is applied, keeping walls uniform on deep draws — often combined with vacuum or pressure forming.
See each method with process diagrams and a "when to use which" guide on types of thermoforming, or our design guide for draft angles, wall thickness and tolerances.
Thin gauge vs thick gauge
Thin gauge (0.1–2 mm)
Roll-fed, high-speed, multi-cavity forming for packaging, trays, blisters, clamshells, cups and lids. Measured in thousands of parts per hour.
Thin gauge capability →Thick / heavy gauge (2–12 mm)
Cut-sheet forming of large, durable single parts — machine covers, EV and appliance panels, medical housings, liners and dunnage — that often replace metal or fibreglass.
Thick gauge capability →Thermoforming materials
Almost any thermoplastic can be thermoformed. These are the workhorses — and because Indu extrudes its own sheet, grade, colour, texture and thickness are controlled from the pellet.
ABS
Tough, stiff, easy to form and finish — housings, panels, automotive trim. FR and UV-stable grades available.
HIPS
Economical, food-safe grades, easy to print — packaging, liners, POS, disposables.
PET / APET / RPET
Glass-clear, food-contact, recyclable and recycled-content — blisters, clamshells, food trays.
PP
Chemical and fatigue resistance, microwavable, barrier (EVOH) options — meal trays, living-hinge parts.
PC / PC-FR
Extreme impact and heat resistance, UL 94 V-0 and CTI 600 grades — EV battery covers, machine guards, electrical insulation.
HDPE
Outdoor durability and chemical resistance — dunnage, tanks, covers, agri.
PMMA-ABS / ASA
UV-stable, weatherable, premium gloss — sanitary ware, RV cladding, appliance fascias, EV exteriors.
PVC / PLA / TPO
Legacy clarity, compostable bio-grades, and soft-touch/flexible options for specialist uses.
See full grade data on our materials & grades page, with downloadable datasheets.
Thermoforming vs injection moulding
The most common sourcing question — here's the honest comparison. Neither wins outright; each dominates a region of the size / volume / detail map.
Rule of thumb: choose thermoforming for large parts, sub-~20,000/year volumes, or parts in weeks; choose injection moulding for very high volumes of small, thick, highly-featured parts.
Where thermoforming is used
Advantages
- Low tooling cost & fast lead times
- Very large parts on a single tool
- Cheap, low-risk design iteration
- Lightweight metal / fibreglass replacement
- FR, ESD, food-grade & recycled options
Limitations
- Single-wall geometry (no solid thick sections)
- Walls thin on very deep draws (managed with plug assist)
- Less fine detail than injection moulding (pressure forming narrows the gap)
- Trimming is a separate step
Is thermoforming sustainable?
Thermoforming offcuts (skeletal scrap) are routinely reground and re-extruded, and recycled-content sheet — RPET and ABA recycled-core constructions — is widely used. Because Indu extrudes its own sheet, recycled and bio-based grades (PLA, bio-PET) can be specified directly and certified.
Thermoforming FAQ
What is thermoforming in simple terms?
Thermoforming is a plastic manufacturing process that heats a flat thermoplastic sheet until it is soft, then uses vacuum and/or air pressure to form it over a mould, cools it to lock the shape, and trims it to the finished part.
What is the difference between thermoforming and vacuum forming?
Vacuum forming is one type of thermoforming — it uses only vacuum to draw the sheet onto the tool. Thermoforming is the umbrella term that also includes pressure forming and plug-assist forming, which add air pressure or mechanical assistance for more detail and deeper draws.
What materials can be thermoformed?
Most thermoplastics: ABS, HIPS, PET/PETG/RPET, PP, PC (including FR grades), HDPE, PMMA-ABS, ASA, PVC and bio-based PLA. Grades are available with flame-retardant (UL 94 V-0), ESD-safe, food-contact (FDA) and UV-stable properties.
What is the difference between thin gauge and thick gauge thermoforming?
Thin gauge uses roll-fed sheet from 0.1–2 mm for high-speed packaging, trays and blisters. Thick (heavy) gauge uses cut sheet from ~2–12 mm for large, durable structural parts such as covers, panels, enclosures and liners.
Is thermoforming cheaper than injection moulding?
For low-to-medium volumes and large parts, yes — thermoforming tooling is typically 10–20% of the cost of an injection mould and ready in 2–4 weeks instead of 12–16. Injection moulding becomes more economical only at very high volumes or for small, thick, highly detailed parts.
How accurate is thermoforming?
Parts are made to ISO 2768 coarse class as standard — e.g. ±0.5 mm up to 30 mm, ±1.2 mm at 120–400 mm — with tighter tolerances agreed on critical features. CNC-trimmed edges and holes are datum-referenced, and wall thickness is kept uniform with pre-stretch, plug assists and sag control.
Is thermoformed plastic recyclable?
Yes. Thermoforming offcuts (skeletal scrap) are regularly reground and re-extruded, and recycled-content sheet (RPET, ABA recycled-core constructions) is widely available. Because Indu extrudes its own sheet, recycled and bio-based grades can be specified directly.
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