What is the Process of 3 Layer Blown Film Extrusion?

Ever wondered how your food packaging, shopping bags, or shrink wraps get that perfect strength, flexibility, and clarity? The answer lies in a smart plastic manufacturing method called 3-layer blown film extrusion.

This process blends science and engineering to create high-performance plastic films used in everything from snacks to shrink-wraps.

But how does it actually work?

Let’s break it down step by step.

What is 3-Layer Blown Film Extrusion?

3-layer blown film extrusion is a manufacturing process used to produce plastic films made up of three distinct layers. Each layer is extruded simultaneously and blown into a thin film tube, then cooled, flattened, and wound into rolls.

Why three layers? Because each layer can be customized for specific properties like:

• Strength

• Barrier protection (oxygen, moisture)

• Printability

• Sealability

This process allows manufacturers to create films that are stronger, more functional, and cost-effective compared to single-layer films.

Key Components of a 3-Layer Blown Film Line

Before we dive into the process, let’s meet the key players:

Main Equipment:

• Three Extruders (one for each layer)

• Die Head (3-layer co-extrusion die)

• Air Ring

• Blown Film Tower

• Nip Rollers

• Take-up System

• Winder

Each part has a specific role in forming the perfect film.

Step-by-Step Process of 3-Layer Blown Film Extrusion

Let’s walk through the full process from raw pellets to finished film roll.

Step 1: Feeding the Extruders

Each layer starts with plastic resin pellets (like LDPE, LLDPE, HDPE, EVOH, or Nylon), fed into three separate extruders.

Customization:

• Layer A: Sealability (e.g., LLDPE)

• Layer B (Middle): Strength or barrier (e.g., HDPE or EVOH)

• Layer C: Printability or stiffness (e.g., LDPE or Metallocene)

The resins may also be mixed with additives for UV resistance, color, slip, anti-blocking, or anti-static properties.

Step 2: Melting the Resin

Inside each extruder barrel, the plastic pellets are heated and mixed until they melt into a homogeneous molten polymer.

• Temperatures typically range from 160°C to 250°C

• Screw design helps mix, melt, and push the material forward

Step 3: Co-Extrusion Through a 3-Layer Die Head

Now comes the magic: The three molten polymers are fed into a 3-layer die head. This die brings all three layers together in a circular format.

How It Works:

• Layer A forms the outer surface

• Layer B becomes the core

• Layer C forms the inner surface

The output is a multi-layer tubular bubble, where all three layers are bonded together during extrusion.

Step 4: Blowing the Bubble

As the molten tube exits the die, air is blown into the center, inflating it like a balloon.

This creates a thin, cylindrical film bubble. The diameter and thickness are controlled by:

• Blow-up ratio (BUR): Ratio of bubble diameter to die diameter

• Haul-off speed

• Air pressure

• Cooling rate

Step 5: Cooling the Film

To stabilize the bubble and set its structure, cooling air rings are used to quickly chill the film.

Why fast cooling? Because it:

• Prevents sagging

• Locks in mechanical properties

• Helps achieve optical clarity

Step 6: Collapsing the Bubble

After cooling, the film bubble is flattened by nip rollers at the top of the tower.

The result? A double-layered sheet (like a folded tube), ready for the next stage.

Step 7: Take-up and Winding

The flattened film is pulled down, slit (if needed), and rolled onto winding drums to form neat film rolls.

Depending on your application, the film can now be:

• Printed

• Laminated

• Bagged

• Converted into various packaging forms

Applications of 3-Layer Blown Films

Why use three layers instead of one? Because each layer can be custom-engineered.

Common Uses:

• Food packaging (snacks, frozen foods, meat, cheese)

• Agricultural films

• Industrial wraps

• Shrink film

• Heavy-duty shipping sacks

• Barrier films (e.g., vacuum packaging)

Advantages of 3-Layer Blown Film Extrusion

Let’s talk about why manufacturers love this method.

Key Benefits:

• Cost-effective: Use cheaper material in one layer, premium in others

• Custom performance: Each layer serves a purpose (e.g., strength, sealing)

• Barrier protection: Oxygen/moisture resistance with barrier resins

• Better machinability: Improved printability, lamination, and bagging

• Higher strength-to-thickness ratio: Thinner films with better properties

Typical Film Structures

Here are a few examples of common 3-layer film combinations:

Who Uses 3-Layer Blown Film Extrusion?

It’s widely adopted by:

• Flexible packaging converters

• Plastic film manufacturers

• Food packaging companies

• Agricultural film suppliers

Whether it’s a local bag maker or a multinational food brand, many rely on this versatile technology.

Final Thoughts: Why 3-Layer Blown Film is the Gold Standard

3-layer blown film extrusion is the backbone of modern flexible packaging. It allows for tailored performance, reduced material costs, and improved sustainability—all in a single process.

If you're in the plastic film industry or exploring film production, investing in 3-layer extrusion can unlock huge versatility and market opportunities. For more information about the machinery used in 3-layer blown film extrusion, check out 3 layer blown film machine.