Extrusion Blow Molding: Manufacturing of Hollow Plastic Bodies
Last updated: 13. March 2026
Extrusion Blow Molding (EBM) is an established plastic processing method for the production of hollow bodies such as bottles, plastic ampoules, or technical containers. It enables the economical production of large quantities and is therefore used in industries such as cosmetics, food, and chemicals.
In the pharmaceutical industry, the process is frequently used as an integral part of Blow-Fill-Seal (BFS) technology. In this process, the container is shaped immediately before filling and sealing in a closed, aseptic system, which reduces the risk of contamination to a minimum.
In this process, a molten plastic is extruded as a tube-like strand – the so-called parison – and subsequently inflated into a hollow body in a closed mold using compressed air. The plastic adheres to the mold walls and solidifies there. A characteristic feature is the combination of continuous extrusion and subsequent shaping in the mold. Another important feature of EBM is the targeted control of material distribution: by adjusting the extrusion gap, the wall thickness along the plastic tube can be varied to concentrate material specifically in highly stressed areas such as the base or shoulder.
Sequence of Extrusion Blow Molding
The production process on Rommelags bottelpack systems consists of several precisely coordinated steps. In contrast to conventional filling lines, which often work with monoblock systems, BFS technology combines forming, filling, and sealing in a single, seamless operation.
- Material Supply and Melting: Plastic granulate is plasticized in the extruder by temperature and mechanical shear forces until a homogeneous melt is produced.
- Extrusion of the Parison: The plastic melt is pressed through an annular die, creating a continuous tube whose wall thickness can be flexibly adjusted.
- Closing of the Mold: The mold closes around the parison, simultaneously forming the neck area and the contour of the future container. Excess material is pinched off.
- Inflation of the Hollow Body: Under aseptic conditions, sterile compressed air or a vacuum is used to press the plastic precisely against the inner walls of the mold. This process takes place within the machine in a controlled cleanroom zone (Class A / ISO 5).
- Cooling and Shape Stabilization: The mold is actively tempered via integrated cooling channels. With BFS technology, the plastic remains sterile because the inside of the container is not exposed to uncontrolled environmental conditions during the entire process.
- Removal and Post-processing: After the mold is opened, the container is removed and the so-called flash (waste material) is removed.
Digitalization: Smart Blowing
With the networking of machines, sensors, and software – often referred to as Smart Blowing – process parameters such as temperature profiles, air supply, and material flow are continuously monitored. The goal is more stable production and predictive maintenance to avoid unplanned downtime. Especially in regulated industries, this digital data acquisition also supports the seamless documentation and validation of processes.
Materials and Applications
Thermoplastics such as polyethylene (HDPE/LDPE) or polypropylene (PP) are predominantly used. The choice of material depends on the mechanical requirements, chemical compatibility with the filling product, and the necessary barrier properties.
Typical applications include:
- Plastic bottles for pharmaceutical solutions
- Sterile single-dose containers for eye drops or inhalation solutions
- Packaging for cosmetic and food products
- Canisters and technical hollow bodies
Advantages and Disadvantages of the Process
The process offers clear advantages:
- Economical production of large quantities
- High flexibility in container shapes and volumes
- Elimination of separate container sterilization: Since the container is formed from the hot melt, the interior is already sterile. External cleaning or pre-sterilization of the packaging is not required.
- Integration into fully automated production lines
Limitations exist for very complex geometries, which may exhibit limited precision. Furthermore, process stability is heavily dependent on constant temperature and pressure conditions.