A Practical Guide to Stretch Film Thickness and Strength

Introduction

What Is Stretch Film?

Stretch film, primarily manufactured from Linear Low-Density Polyethylene (LLDPE), is the ubiquitous standard for unitizing pallet loads in modern supply chains. Unlike shrink wrap, which requires heat to shrink around a product, stretch film relies on its inherent elastic memory. When the film is elongated (stretched) and applied to a load, it attempts to return to its original state. This elastic recovery creates a compressive force known as containment force that holds the load together during transit.

Why Thickness and Strength Matter in Packaging

In warehouse operations, the margin for error is slim. Selecting the incorrect film thickness or strength profile leads to two costly extremes:

1. Load Failure: Weak or under-gauged film results in pallet shifting, product damage, and safety hazards during transport.

2. Material Waste: Over-specifying film thickness (using a 23-micron film where a high-performance 12-micron film would suffice) inflates packaging costs without adding necessary value.

Optimising film specifications is not merely a purchasing decision; it is an operational necessity that impacts throughput speed, waste generation, and the total cost per pallet wrapped.

Overview of Stretch Film Performance Factors

Evaluating stretch film requires moving beyond simple thickness measurements. A holistic assessment includes yield strength (how much it can stretch before permanent deformation), puncture resistance (vital for irregular loads), and cling (the ability of layers to adhere to one another without sticking to adjacent pallets). Understanding the interplay between these factors is essential for maintaining supply chain integrity.

Understanding Stretch Film Thickness

What Is Stretch Film Gauge and Micron?

The industry uses two primary units of measurement for film thickness, often leading to confusion in procurement: Gauge and Micron.

• Gauge: The standard unit of measurement in North America.

• Micron (µm): The metric unit used globally and in scientific specifications.

One micron is one-millionth of a metre. One gauge unit is equal to one hundred-thousandth of an inch. While these numbers seem microscopic, a variance of just a few microns significantly alters the film's holding power and yield.

Gauge vs Micron Conversion Chart

For procurement officers dealing with international suppliers or diverse machinery specs, accurate conversion is critical.

Common Thickness Ranges and Their Uses

• Standard Gauge (60-80 ga / 15-20 µm): The workhorse of the industry. Suitable for uniform loads (Type A) like boxed goods stacked squarely on a pallet.

• Performance/High-Performance Gauge (variable): Modern nanotechnology allows thinner films (e.g., 12 µm) to perform with the strength of traditional 20 µm films. These are used to reduce plastic consumption while maintaining load stability.

• Heavy Gauge (100 ga+ / 25 µm+): Reserved for Type C loads containing sharp edges, heavy machinery parts, or bricks where puncture resistance is the priority over yield.

How Thickness Affects Load Stability

Historically, thicker film equalled better stability. This is no longer strictly true due to resin advancements. However, thickness still correlates with stiffness. A thicker film generally has a higher modulus of elasticity, meaning it resists stretching more aggressively. For extremely heavy loads (excess of 1,000 kg), a thicker film provides the necessary rigidity to prevent the load from swaying, assuming the application equipment can apply enough tension to utilize that stiffness.

Understanding Stretch Film Strength

Tensile Strength Explained

Tensile strength refers to the maximum stress the film can withstand while being stretched before breaking. In a machine environment, high tensile strength is vital to prevent film snaps during the wrap cycle, which causes downtime. A film with high tensile strength allows for tighter wrapping, increasing the containment force on the pallet.

Puncture Resistance and Tear Resistance

These are distinct but related properties:

• Puncture Resistance: The ability to withstand a sharp object (like the corner of a pallet or a protruding nail) pressing into the film without rupturing.

• Tear Resistance: The ability of the film to resist the propagation of a tear once a puncture has occurred. High-quality films, particularly "blown" films, prevent a small hole from "zippering" across the entire width of the web, ensuring the integrity of the wrap remains even if minor damage occurs.

Load Retention Force and Elastic Recovery

Load containment force is the single most critical metric in pallet stability. It is the cumulative force the film exerts on the load.

• Elastic Recovery: This is the "rubber band" effect. If a film is stretched 200%, it wants to return to 0%. That return energy holds the boxes in place.

• Stress Relaxation: Over time (especially during the first 24 hours), film relaxes and loses some holding force. High-quality films have lower stress relaxation rates, ensuring the pallet arrives at the destination as tight as it left the warehouse.

Stretchability and Elongation at Break

Elongation at break is the point at which the film snaps. However, the yield point is more practically relevant—this is the maximum stretch percentage the film can handle while still maintaining its ability to recover.

• Standard films may stretch 150-200%.

• High-performance machine films can stretch 300-400%. Utilising the correct pre-stretch gear ratio on wrapping machines is crucial to leverage this potential without snapping the film.

Types of Stretch Film by Performance

Hand Stretch Film

Designed for manual application, hand rolls are lighter and shorter (typically 1,000–1,500 ft).

• Characteristics: Lower stretch potential (usually max 100-150%) because human operators cannot generate the tension required to stretch high-performance films.

• Use Case: Low-volume operations (<15 pallets/day) or decentralized packaging areas.

Machine Stretch Film

Engineered for use on semi-automatic and automatic rotary arm or turntable wrappers.

• Characteristics: High stretch capability (200-300%+).

• Advantages: consistent application tension, reduced material usage via pre-stretch carriages, and significantly higher containment force than hand wrapping.

Pre-Stretched Film

This film is stretched near its breaking point during manufacturing and wound onto the roll in a stretched state.

• Advantages: It requires minimal physical effort to apply (excellent for workforce ergonomics) and provides consistent yield. Because it is already stretched, it offers superior neck-down resistance (width maintenance).

• Disadvantages: Lower residual elasticity compared to machine-stretched film.

Blown vs Cast Stretch Film

The manufacturing process dictates the film's molecular structure.

• Cast Film (Extrusion): The industry standard. Produced by cooling molten resin on a chill roll. It is clear, quiet to unwind, and has excellent tear resistance. Ideally suited for barcode scanning.

• Blown Film: Produced by blowing air into a ring of molten plastic. It is tougher, has superior puncture resistance, and higher cling. However, it is hazy, noisy during unwind, and typically more expensive. Used for heavy, irregular, or sharp loads.

How to Choose the Right Thickness and Strength

Evaluating Load Weight and Dimensions

Classify your load profile:

• Type A: Uniform shape, no sharp edges (e.g., stacked identical cartons). Recommendation: Thinner, high-performance cast film.

• Type B: Irregular stacking, some variance in layer size. Recommendation: Medium gauge, focus on puncture resistance.

• Type C: Very irregular, sharp protrusions, or unstable dimensions. Recommendation: Heavy gauge or blown film.

Assessing Transportation Conditions

The mode of transport dictates the G-forces the load will endure.

• Internal Transport: Low stress; lighter gauge acceptable.

• Road Transport (LTL): High vibration and braking forces. Requires high containment force and puncture resistance to survive cross-docking.

• Rail/Sea: Long-duration transit with significant swaying. Requires films with high elastic recovery to combat settling over time.

Matching Film Type to Application

Do not use machine film for hand wrapping; the operator cannot stretch it enough to activate the "memory," resulting in a loose load. Conversely, using hand film on a high-speed machine will result in frequent snaps and downtime.

Cost vs Performance Considerations

Metric to watch: Cost Per Pallet. Buying the cheapest roll (Price per kg) often leads to higher costs. A "cheap" standard film might require 12 oz of plastic to secure a load, whereas a premium, stronger, thinner film might secure the same load with 6 oz. Even if the premium roll costs 20% more, the 50% material reduction results in significant net savings.

Industry Applications

Warehouse and Logistics

High-volume distribution centres require machine films capable of 250%+ pre-stretch to maximize throughput and minimize roll changes. Consistency is key here to prevent automated system stoppages.

Food and Beverage Industry

• Beverage: Bottled liquids are heavy and settle during transit. Films with ultra-high elastic recovery are required to maintain tension as the load shifts.

• Perishables: Macro-perforated or "breathable" stretch films are often used to allow airflow and prevent condensation/spoilage, requiring higher gauge bands to maintain strength despite the holes.

Construction Materials

Bricks, pavers, and roofing shingles are heavy and abrasive. This is the domain of heavy-gauge (25-30 micron) blown film. Clarity is secondary to the sheer ability to prevent the film from shredding against rough concrete surfaces.

E-commerce and Retail Distribution

Retail distribution involves "rainbow pallets"—mixed loads of varying shapes and weights. These are notoriously difficult to wrap. High-performance films with multi-layer nanotechnology (sometimes 30+ layers) provide the versatility to wrap a heavy detergent box next to a fragile crisp box without crushing the latter or dropping the former.

Common Mistakes to Avoid

Using Thicker Film Than Necessary

"Thicker is safer" is a fallacy. Using an 80-gauge film where a high-performance 50-gauge would work wastes plastic and money. It also increases the carbon footprint of the operation.

Ignoring Load Profile and Sharp Edges

Applying high tension to a load with sharp corners without using a puncture-resistant film results in film failure at the corners (the highest stress point).

• Solution: Use films with high tear propagation resistance or apply corner boards before wrapping.

Incorrect Stretch Settings on Machines

If a machine is set to 250% pre-stretch but is loaded with a film rated for 200%, the film will micro-fracture (called "tiger striping"). This destroys the film's holding power. Regular machine calibration is essential.

Overlooking Environmental Factors

Standard stretch film degrades under UV light. If pallets are stored outdoors or transported on open flatbeds, UV-stabilized film must be used. Standard film can become brittle and fail within weeks of sun exposure.

FAQs

What Is the Best Thickness for Pallet Wrapping?

There is no universal "best." For standard Type A loads (uniform boxes, <800kg), a 17-20 micron (70-80 gauge) film is standard. However, high-performance 12-15 micron films can often replace these. The best thickness is the minimum gauge required to achieve the necessary containment force without failure.

Does Thicker Stretch Film Mean Stronger?

Not necessarily. Strength is defined by the resin formulation and extrusion technology. A modern, multi-layer 15-micron film can have higher puncture resistance and tensile strength than an older technology 23-micron film. Thickness correlates with stiffness, but not always holding power.

How Do I Measure Stretch Film Thickness?

You must use a calibrated micrometer. Because film thickness varies slightly across the web, measure the film at the edges and the centre to get an average. Ensure you measure the film off the roll before it has been stretched.

What Is the Difference Between Gauge and Micron?

They are simply different units of measurement for the same physical property.

• 1 Gauge = 0.254 Microns.

• To convert Gauge to Micron: Divide Gauge by 4 (approximate) or multiply by 0.254 (precise).

• To convert Micron to Gauge: Multiply Micron by 4 (approximate) or 3.937 (precise).

Conclusion

Key Takeaways for Selecting the Right Stretch Film

The integrity of your supply chain relies on the few ounces of plastic wrapped around your pallets. Selection should be based on:

1. Containment Force: The actual pressure holding the load.

2. Load Profile: The weight, shape, and sharpness of the goods.

3. Stretch Capability: Matching the film specifications to your equipment's pre-stretch gears.

Final Recommendations for Cost-Effective Packaging

To achieve true cost efficiency, shift the focus from "Cost per Roll" to "Cost per Pallet Wrapped." Conduct a cut-and-weigh audit: wrap a pallet, cut the film off, and weigh it. Compare the weight and load stability of different films. Often, upgrading to a stronger, thinner, high-tech film reduces plastic consumption by 20-30%, lowering total costs and environmental impact while improving load security.