PROFESSIONAL BLOG
NOVEMBER 16, 2024 • 8 MIN READING
Twin Sheet – hollow and dense, without glue
Twin Sheet is an advanced variant of vacuum forming that allows us to create hollow, double-walled products with high strength and low weight – in one and the same workpiece, without glue or joining.
Jon Jørundland
COO Plexx
What is Twin Sheet production?
Twin Sheet is a specialized form of vacuum forming in which two separate thermoplastic sheets are heated simultaneously and then formed and joined into one part. The two sheets are bonded together during forming, creating a hollow core or double wall structure.
The process combines the advantages of traditional vacuum forming with significantly increased structural strength, enabling complex designs with great precision – in materials such as PE, PP, ABS and PVC.
THE EDGES ARE MELT TOGETHER UNDER PRESSURE
How are Twin Sheet products manufactured?
01
Choice of materials
PE for flexibility and impact resistance, ABS for high surface quality, PP for low weight and good chemical resistance.
02
Heating the plates
Two sheets are heated simultaneously to a precise forming temperature. The correct temperature is critical for strength and surface finish.
03
Forming and joining
The plates are placed in a double-sided mold. Vacuum pulls them towards each side, and the edges are fused together under pressure.
04
Cooling and post-processing
Controlled cooling provides correct mechanical properties. Trimming, drilling and assembly are done after forming.
“Twin Sheet manufacturing is an advanced and versatile method for creating plastic products with high strength, low weight and complex geometric shapes.”
The advantages of Twin Sheet
High strength, low weight: Double walls provide rigidity – hollow core keeps weight down.
Cost-effective: Lower tooling costs than injection molding, well suited for medium-sized series.
Design flexibility: Integrated handles, ribs and channels in one operation.
Insulating: Hollow core provides both thermal and acoustic insulation.
Less retrofitting: Reinforcements are cast in – saving time and strengthening the structure.
HOLLOW CORE BETWEEN TWO SHAPED PLATES
Applications for Twin Sheet
The automotive industry
Protective panels, door panels, air ducts – strong and lightweight components that help reduce fuel consumption.
Packaging and logistics
Transport crates, pallets and protective units with built-in reinforcements and space for fragile goods.
Medical products
Beds, examination tables and cabinets – load-bearing and lightweight, with surfaces that are easy to clean.
Construction industry
Building panels, partitions and insulation elements that combine strength with thermal and acoustic insulation.
Twin Sheet Challenges
Twin Sheet requires precise temperature control – both sheets must be at exactly the right temperature for the joint to be strong and consistent. Custom shapes can also be expensive, making the method rarely economically viable for very small runs.
With the right equipment, trained operators and well-thought-out tools, Twin Sheet is still a profitable solution for a wide range of technical products.
Questions and answers about Twin Sheet
Conventional vacuum forming uses a single sheet stretched over a mold. Twin Sheet uses two sheets that are heated simultaneously and formed against each other by a double-sided tool, before being fused together at the edges. The result is a hollow, double-walled product — made in one operation, without glue, welding or other joining. This provides both a better strength-to-weight ratio and the possibility of integrated insulation in the same part.
The most common are polyethylene (PE) for flexibility and impact resistance, polypropylene (PP) for low weight and good chemical resistance, ABS for high surface quality and processability, and PVC where flame retardancy is required. We can also work with technical thermoplastics and special materials where the application requires it — for example, UV-stabilized or flame-retardant quality.
A Twin Sheet construction with two sheets and a hollow core provides significantly higher bending stiffness than a single sheet of the same total weight. The principle is the same as in an I-beam: the distance between the two “flanges” (sheets) provides the stiffness. In practice, this means that we can often halve the weight compared to a solid construction — or build much larger parts without increasing the weight correspondingly.
Yes. The hollow core can be filled with PUR foam for increased rigidity, better thermal insulation or vibration and sound damping. We can also integrate inserts such as metal sleeves, fixing points, ribs and channels directly into the process, so that the final product requires little or no retrofitting.
Tolerances are at the same level as in other vacuum forming — typically ±0.5 mm depending on geometry, material and tool. The surface on the outside of the sheets is smooth and gets its texture from the raw material (e.g. glossy, matt or structured). The inside — which lies against the tool — can be given the desired surface and level of detail. Sharp geometries and tight tolerances are often solved by combining Twin Sheet with CNC milling of holes, edges and attachment points after forming.
For medium-sized runs (typically a few hundred to a few thousand units per year) of large, hollow or double-walled products, Twin Sheet is often the most sensible choice. Tooling costs are significantly lower than injection molding, and the process handles larger dimensions. For very high volumes or small, complex parts, injection molding is still more cost-effective — we always consider both methods against each other when providing quotes.
We follow the same capacity as other vacuum forming processes — up to 1300 × 1850 mm with a depth of up to 300 mm. This makes Twin Sheet suitable for large components such as pallets, transport containers, ventilation parts, building panels and covers for vehicles and construction machinery.
Once the design and material selection are finalized, it typically takes 6–10 weeks to build a double-sided tool and start production. Early involvement in the design phase — through DFM assessment — can reduce both lead time and tooling cost, because we can adapt geometry, radii, and wall thickness to the process before the tool is built.
The thermoplastics we use are 100% recyclable, and the entire construction consists of the same or compatible materials — making recycling easy at end-of-life. Low weight reduces transportation emissions, and the long lifespan of Twin Sheet products (often 15–20 years for pallets, crates and building panels) results in a low carbon footprint per year of use.
Do you have questions about Twin Sheet?
We help you through the entire process – from design to finished product. Contact us to see how we can help you with your production.