Archive entry · 2026-05-08
Historical content; not current machine specifications or a production guarantee.
When you need a large plastic part, two processes compete: thermoforming and rotomoulding. Here's how to choose correctly.
When you need a large plastic part — a water tank, a kayak hull, a playground slide, a vehicle body panel — two processes compete for the job: thermoforming and rotational moulding (rotomoulding). Both handle big parts. Both use relatively inexpensive tooling compared to injection moulding. But they produce fundamentally different parts, and choosing wrong costs you years of suboptimal production. This is the honest comparison.
A flat sheet of thermoplastic is heated, then drawn against a single-sided mould using vacuum and/or pressure. The sheet conforms to the mould shape, cools, and is trimmed. Cycle times are measured in minutes (typically 2–10 minutes for heavy-gauge parts). The process starts with extruded sheet — the material has already been processed once before forming.
Powdered plastic (usually polyethylene) is loaded into a hollow mould, which is then heated while rotating on two axes simultaneously. The powder melts and coats the inside of the mould uniformly. The mould cools while still rotating, and the hollow part is extracted. Cycle times are measured in tens of minutes to hours (typically 15–60 minutes). The process starts with powdered resin.
This is the single biggest differentiator. Rotomoulding produces completely enclosed hollow parts — water tanks, fuel tanks, kayaks, playground equipment. Thermoforming produces open shell parts — panels, trays, enclosures, liners. If your part must be a sealed hollow vessel, rotomoulding. If your part is an open shell or panel, thermoforming.
Thermoforming: 2–10 minutes per cycle for heavy-gauge parts. Rotomoulding: 15–60 minutes per cycle. For volume production, thermoforming produces five to twenty times more parts per shift. If you need more than a few thousand parts per year, thermoforming's speed advantage compounds significantly.
Rotomoulding: primarily polyethylene (LLDPE, HDPE, XLPE). Limited material range because the powder must melt and flow uniformly during rotation. Thermoforming: ABS, HIPS, HDPE, PP, PET, PMMA, PC, PVC, TPO, and multi-layer laminates. Much broader material palette because the process starts with pre-extruded sheet.
Rotomoulding produces relatively uniform wall thickness (the powder distributes evenly during rotation). Thermoforming produces variable wall thickness (thinner at deep draws, thicker at shallow areas). For structural applications requiring uniform walls, rotomoulding has an inherent advantage. For applications where variable thickness is acceptable, thermoforming is fine.
Thermoforming produces excellent surface quality on the mould side — Class A automotive finishes are achievable. Rotomoulding produces a textured surface (orange-peel effect) that's acceptable for industrial products but not for cosmetic applications. If surface appearance matters to your end customer, thermoforming wins decisively.
Both processes use tooling that should be evaluated against geometry, material, volume, surface, and workflow requirements. Confirm tooling scope and costs with the relevant supplier.
Open-shell parts (panels, trays, enclosures, liners). Higher production volumes (above 2,000 per year). Surface quality matters (automotive, consumer products, sanitaryware). Broad material requirements (ABS, PMMA, multi-layer). Fast cycle times needed. Parts requiring precise dimensional control.
Explore Machinecraft's large-part thermoforming: PF1-XL series (up to 6000×2200 mm) → | PF1-X series → | Dutch horticulture trays on PF1-XL →
Completely enclosed hollow parts (tanks, vessels, floats). Very low volume (under 500 per year). Uniform wall thickness critical. Parts requiring no seams or joints. Large hollow parts where thermoforming would require two halves bonded together.
Some applications genuinely work with either process: large industrial enclosures, vehicle body components, agricultural equipment housings. In the overlap zone, the decision usually comes down to: volume (thermoforming wins above 2,000/year), surface quality (thermoforming wins), and whether the part needs to be sealed hollow (rotomoulding wins).
See also: Thermoforming process explained → | ROI Calculator → | Request a quote →
Yes, through twin-sheet thermoforming — two sheets are formed simultaneously and fused together at the edges to create a hollow structure. This is used for pallets, structural panels, and some vehicle components. However, twin-sheet parts have a visible seam line and cannot achieve the seamless hollow geometry that rotomoulding produces.
Thermoforming generates trim scrap (typically 15–30% of the sheet) but this is usually regrind-compatible and recycled in-house. Rotomoulding generates minimal scrap but uses more energy per part due to longer cycle times and the need to heat the entire mould mass. Neither process has a clear environmental advantage — it depends on your energy source and scrap-recycling capability.
Thermoforming: up to 6000×2200 mm forming area (Machinecraft PF1-XL series). Rotomoulding: up to approximately 4000×3000×2000 mm for the largest shuttle machines. Both processes can handle genuinely large parts, but thermoforming has the edge on maximum single-dimension size.
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