High vs Low Pressure Blown Film Machines: Which One Fits Your Production Line?

This article explores the key differences between high-pressure and low-pressure blown film machines, covering working principles, application scenarios, technical parameters, and selection tips. A detailed comparison table and real-world use cases help you make an informed decision for your film pr

Understanding High/Low Pressure Blown Film Machines

Blown film extrusion is a widely used process for manufacturing plastic films. The high/low pressure blown film machine refers to two distinct types of equipment designed for different material characteristics and film properties. Choosing between them depends on your target product, throughput requirements, and budget constraints. This guide breaks down everything you need to know.

Working Principles

Both machines share the same basic extrusion process: plastic pellets are melted, extruded through a circular die, and inflated with air to form a bubble, which is then cooled and wound. The key difference lies in the screw design, die head pressure, and cooling system.

High pressure blown film machine: Uses a screw with a higher compression ratio (typically 3.0–4.0) to generate greater melt pressure. The die head is designed to withstand pressures of 60–100 MPa. This allows processing of materials with higher viscosity, such as HDPE, and produces films with better mechanical strength and clarity.
Low pressure blown film machine: Operates with a lower compression ratio (2.0–2.8) and die head pressure around 30–50 MPa. It is optimized for materials like LDPE, LLDPE, and blends. The lower pressure reduces energy consumption and is gentler on heat-sensitive resins, making it ideal for thin films and multi-layer structures.

Technical Parameter Comparison

The table below summarizes the typical specifications for both types of machines in medium-sized production lines.

Parameter	High Pressure Machine	Low Pressure Machine
Screw Diameter (mm)	55 – 90	45 – 75
L/D Ratio	30:1 – 35:1	28:1 – 32:1
Compression Ratio	3.0 – 4.0	2.0 – 2.8
Max Die Head Pressure (MPa)	80 – 100	35 – 50
Main Motor Power (kW)	22 – 55	15 – 37
Output (kg/h)	40 – 120	30 – 90
Film Thickness Range (μm)	15 – 120	8 – 60
Max Film Width (mm)	600 – 1600	400 – 1400
Typical Materials	HDPE, MDPE, PP	LDPE, LLDPE, EVA
Cooling Type	Air ring + internal bubble cooling	Air ring (single or dual lip)

Application Scenarios

High Pressure Machines Are Best For:

Heavy-duty films: Woven bag liners, shrink film, and construction vapor barriers.
High clarity films: Packaging films requiring high transparency and gloss.
Single-layer HDPE films: T-shirt bags, grocery sacks, and merchandise bags.

Low Pressure Machines Excel In:

Thin films: Stretch film, cling film, and agricultural mulch film.
Multi-layer co‑extrusion: Up to 5 layers for barrier films or soft-touch packaging.
Heat-sensitive resins: EVA, metallocene LLDPE, and recycled blends.

How to Choose?

Consider the following factors when selecting a blown film machine:

Material type: If you mainly process HDPE or PP, a high pressure machine is recommended. For LDPE/LLDPE blends, low pressure is more efficient.
Film thickness: For films below 30 μm, low pressure machines offer better bubble stability and thickness uniformity.
Output volume: High pressure machines generally provide higher output for thick films, but low pressure machines can run faster for thin films.
Energy cost: Low pressure machines consume 15–20% less energy per kilogram of film, a significant factor for large-scale production.
Budget & maintenance: Low pressure machines are typically simpler in construction, leading to lower initial investment and easier maintenance.

Future Trends

Modern high/low pressure blown film machines are increasingly incorporating servo drives, automatic die gap adjustment, and IoT-based monitoring to improve precision and reduce waste. Multi-layer co-extrusion technology is also blurring the line between the two types, with some hybrid machines capable of switching between high and low pressure modes by changing screws and dies.

For most applications, a dedicated high pressure or low pressure machine remains the most cost-effective solution. However, if your production needs vary widely, investing in a versatile machine with interchangeable components might be worth the higher upfront cost.