PROFESSIONAL BLOG
FEBRUARY 12, 2025 • 5 MIN READING
Rotational molding – for large, hollow and durable plastic products
Plexx offers various solutions within plastic rotational molding, either with CNC or manual machining. We are happy to provide special machines and automated processes with robots for larger assignments.
Espen Johansen
Project Engineer Plexx
There are several things that make rotational molding unique as a plastics manufacturing method. The process uses powdered plastic that is heated and rotated in a closed tool around two axes. The result is large, hollow, seamless parts with uniform wall thickness – without welds or weak spots.
Production of cavities without joints
Rotational molding creates hollow parts without any joints, which increases strength and prevents leaks. The entire product is molded in one continuous process, so there are no weak points where the material is joined.
The method is often used for water tanks, chemical containers and fuel tanks – products where tightness and structural integrity are absolutely essential.
Cost-effective for small and medium series
Compared to injection molding, rotational molding has significantly lower tooling costs. The molds are made of aluminum or steel, and the process does not require the extremely high pressure that characterizes other methods.
This makes the method perfect for custom products and smaller series, where investment in expensive injection molds cannot be justified. From a few dozen to a few thousand units per year, rotational molding is often the most profitable choice.
Thicker and more durable walls
Rotational casting provides uniform wall thickness across the entire product, with less risk of weak spots. Extra thickness at corners and edges occurs naturally in the process and provides increased durability precisely where the stress is greatest.
The result is impact-resistant and robust products that can withstand rough handling – perfect for industry, agriculture and transport.
Possibility of complex shapes and large products
Rotational molding is often used for products that are several meters in size. There are no practical limitations on design – you can create asymmetrical or complex shapes that are difficult or impossible to produce with other methods.
Everything from kayaks and boat hulls to playground equipment, furniture and large industrial containers are produced using this method.
Material flexibility and recycling
Rotational molding uses durable thermoplastics. The most common is polyethylene (PE), which is resistant to weather, UV radiation and chemicals. PE and other materials can be fully recycled and reused at the end of their life.
Additives can be used to achieve UV resistance, chemical resistance, antistatic properties and fire retardant properties – tailored to the specific application.
Production without high pressure = less material stress
Unlike injection molding and extrusion, rotational molding does not use high pressure. This means that no internal stresses are created in the plastic – resulting in stronger, more flexible products with better long-term performance.
No risk of air bubbles or weaknesses provides better quality and durability over time.
Typical products made with rotational molding
Water tanks, septic tanks, chemical containers
Coolers and freezers
Playground equipment and slides
Kayaks, canoes and boat hulls
Traffic signs, road and safety barriers
Large plastic covers and panels for machines
Purchasing and logistics
The solution is individually agreed with our customers based on their needs and wishes. Many customers choose to use us as a total supplier.
For example, with total solutions, you can supply the parts yourself, which we then assemble on or with the finished plastic component. Alternatively, we can also handle the purchasing and logistics of the necessary parts.
Our mold and tool department, staffed with skilled employees, produces rotational molding molds as well as milling and machining fixtures.
"Rotational molding is an ideal production method for large, hollow, and durable plastic products. It offers lower tooling costs, great design freedom, and high durability."
Frequently asked questions
The most common material is polyethylene (PE) — both LLDPE and HDPE. Other options include cross-linked PE (XLPE) and polypropylene (PP), depending on temperature and chemical resistance requirements.
There is no fixed upper limit. We regularly produce parts with volumes of several thousand liters and dimensions of several meters.
The wall thickness is usually between 3 and 12 mm, and can be adjusted throughout the entire geometry of the product.
Yes. The thermoplastics used (especially PE) are 100% recyclable and can be melted down into new raw materials.
Rotational molding is advantageous when you need hollow, large parts in small to medium series. Tooling costs are significantly lower than for injection molding.
Do you have questions about rotational molding?
We help you through the entire process – from design to finished product. Contact us to see how we can help you with your production.