Raw Material Selection

Packaging film production starts with polymer resin pellets selected for the required strength, flexibility, clarity, sealability, and barrier performance. Common materials include polyethylene (PE), polypropylene (PP), polyester (PET), polyvinyl chloride (PVC), and specialty biodegradable polymers.

The resin is supplied as small, uniform pellets. Before extrusion, the pellets may be blended with additives, color concentrates, recycled content, or other polymers. In multilayer packaging, each layer can use a different resin so the finished film provides a combination of properties that one material cannot deliver alone.

Resin Pellets

Polyethylene is widely used for flexible packaging because it is flexible, lightweight, heat-sealable, and resistant to moisture. Low-density polyethylene (LDPE) is commonly selected when softness and flexibility are important. Linear low-density polyethylene (LLDPE) provides improved puncture resistance and tensile strength, making it suitable for stretch film, heavy-duty bags, and industrial packaging.

Polypropylene offers higher stiffness, good clarity, and greater heat resistance than many polyethylene grades. Biaxially oriented polypropylene, or BOPP film, is stretched in two directions to improve strength, optical properties, and dimensional stability.

PET film is used when you need high tensile strength, heat resistance, dimensional stability, and a strong printing surface. It is often used as an outer layer in laminated packaging rather than as a heat-sealing layer.

Additives

Additives are blended into the polymer to give the film specific processing or performance characteristics. The correct additive package depends on the product, packaging equipment, storage conditions, and applicable regulations.

Common additive functions include:

For food, pharmaceutical, and medical packaging, additives must be suitable for the intended application and used within permitted limits. You should verify the resin and additive documentation before approving a film for direct product contact.

Film Extrusion

Film extrusion converts plastic resin pellets into a continuous film. The pellets are fed into an extruder, where a heated barrel and rotating screw melt and mix the polymer. The molten plastic is then pushed through a die that determines the initial shape of the film.

After exiting the die, the film is cooled, stabilized, measured, and wound into a master roll. During production, the manufacturer controls temperature, screw speed, extrusion pressure, cooling conditions, film width, thickness, and winding tension.

Blown Film Method

In blown film extrusion, the molten polymer passes through a circular die and forms a vertical tube. Air is introduced inside the tube, inflating it into a large bubble. External air rings cool the bubble as it rises, and rollers then collapse it into a flat double-layer film.

The collapsed film is commonly called layflat film. It can be kept as a tube, opened on one or both sides, or slit into separate webs depending on the final packaging format.

The blown film process is well suited to flexible PE film because it can produce strong, flexible material with good puncture resistance. Film properties can vary across the machine direction and transverse direction, so quality control normally includes testing in both directions.

Important blown film controls include:

1. Die gap and melt temperature, which affect thickness and extrusion stability
2. Blow-up ratio, which influences orientation and film width
3. Cooling air volume, which affects bubble stability and production speed
4. Take-up speed, which influences the final thickness
5. Winding tension, which affects roll hardness and telescoping

Blown film is commonly used for shopping bags, garbage bags, agricultural film, stretch film, shrink film, industrial liners, and flexible food packaging.

Cast Film Method

In cast film extrusion, molten polymer is forced through a flat die to create a wide sheet. The sheet travels directly onto a chilled casting roller, where it cools and solidifies quickly. The film is then trimmed, inspected, and wound.

Cast film usually provides excellent thickness uniformity, smoothness, and clarity. It is also suitable for high-speed production because the film cools rapidly on the chilled roller. Compared with blown film, cast film often has lower shrinkage and more consistent optical quality.

The cast process is frequently used for stretch film, clear packaging film, label stock, medical film, and multilayer structures. The cooling roller temperature, air gap, die design, and line speed must be controlled carefully to prevent wrinkles, gauge variation, and surface defects.

Coating, Printing, and Lamination

Extrusion creates the base film, but many packaging applications require additional processing. Printing adds graphics and product information. Coating improves sealing, barrier performance, or surface functionality. Lamination bonds two or more webs to create a multilayer packaging structure.

These processes are selected according to the packaging machine, product sensitivity, shelf-life target, and required appearance. A finished pouch, for example, may combine a printable PET outer layer, an aluminum or metallized barrier layer, and a PE sealing layer.

Printing

Packaging film is commonly printed using flexographic or gravure printing. The selected method depends on the print quality, design complexity, volume, film type, and required color consistency.

Before printing, the film surface may need treatment. Polyolefin films such as PE and PP have relatively low surface energy, which can make ink adhesion difficult. Corona treatment increases surface energy and helps ink bond to the film.

Printing quality is checked through:

You should confirm whether the film is printed on the outside or between laminate layers. In reverse printing, the image is printed on the inner side of a clear outer film and protected by the laminate. This can improve resistance to scratching and handling damage.

Coating

Coating applies a thin functional layer to the film surface. Depending on the formulation, the coating may improve heat sealing, oxygen resistance, grease resistance, printability, or adhesion to another material.

Typical coating materials include acrylic coatings, PVDC, EVOH-containing structures, water-based coatings, solvent-based coatings, and heat-seal coatings. Each material has specific processing and regulatory requirements.

Coating thickness must be controlled because an uneven coating can cause inconsistent sealing, poor barrier performance, blocking, or appearance defects. The coating process may also require drying ovens, solvent recovery systems, or controlled humidity.

Lamination

Lamination bonds multiple films together to combine their individual properties. A single film may not provide enough strength, barrier protection, printability, and heat sealability at the same time. A laminated structure allows each layer to perform a specific function.

A typical flexible packaging structure may include:

1. Outer layer: Provides printability, stiffness, and abrasion resistance
2. Barrier layer: Limits the transfer of oxygen, moisture, light, or aroma
3. Tie layer or adhesive: Bonds materials together
4. Inner sealant layer: Forms the heat seal that closes the package

Common lamination methods include adhesive lamination, extrusion lamination, and solventless lamination. The adhesive system must be compatible with the film surfaces and the final product. For food and pharmaceutical packaging, curing time and residual solvent requirements are particularly important.

Slitting and Finishing

Large master rolls are too wide for most packaging machines, so they are processed into narrower rolls during slitting. The slitting machine cuts the web to the required width and rewinds each section onto a core.

Slitting accuracy affects the performance of the customer’s packaging line. Incorrect width, uneven edges, loose winding, or telescoped rolls can cause feeding problems, registration errors, web breaks, and sealing defects.

Slitting

During slitting, the operator controls:

The finished roll should have clean edges and consistent winding from the core to the outside diameter. Excessive tension can stretch or deform the film. Insufficient tension can create loose rolls, wrinkles, and telescoping.

Winding and Inspection

After slitting, the film is wound onto paper, plastic, or metal cores. The roll label normally identifies the material, thickness, width, length, batch number, production date, and winding direction.

Quality inspection may include:

Film rolls should be stored in a clean, dry environment away from direct sunlight, heat sources, and chemicals. Temperature changes can affect roll dimensions, blocking, and sealing performance.

How to Check GSM of Plastic Film

You can check the GSM of plastic film by calculating it from thickness and density or by weighing a sample with a standard GSM cutter. The physical method measures the actual mass per unit area, while the mathematical method provides an estimated value based on the film’s nominal thickness and material density.

GSM means grams per square meter. It describes how much one square meter of film weighs. GSM is useful for quality control, material costing, order verification, and comparing film constructions.

For monolayer film, GSM generally increases when thickness increases. However, GSM does not by itself describe all aspects of film performance. Two films with the same GSM may have different tensile strength, sealability, clarity, barrier properties, or puncture resistance.

Method 1: Mathematical Calculation

When you know the film thickness in microns and the polymer density in grams per cubic centimeter, you can estimate GSM using this formula:

This relationship works because one micron of material covering one square meter has a volume that corresponds to the thickness value used in the calculation.

For example, if an LDPE film has a thickness of 25 microns and an estimated density of 0.92 g/cm³:

The result is approximately 23 grams per square meter.

The calculation becomes less precise when the film contains fillers, coatings, inks, adhesives, metallization, or several polymer layers. For a laminate, you should calculate each layer separately when accurate material costing or product specifications are required.

Method 2: Physical Measurement Using a GSM Cutter

A physical GSM test uses a circular cutter with a known cutting area and a precision digital balance. The common cutter area is 100 cm², which equals 1/100 of a square meter.

Place the film flat on a suitable cutting surface and use the cutter to remove a clean sample. Weigh the sample in grams, then multiply the result by 100.

Formula:

For example, if a 100 cm² film sample weighs 0.76 grams:

The film sample should be free from folds, wrinkles, dirt, and excess edge material. If the film is printed, coated, or laminated, the physical test measures the GSM of the complete finished structure.

For better process control, take samples from several positions across the roll width and, when necessary, from the beginning, middle, and end of the roll. A single sample may not reveal cross-web thickness variation.

GSM Test Controls

To obtain repeatable results, you should control the test conditions and equipment. The balance should be calibrated or checked with a known reference weight, and the cutter blade should remain sharp enough to produce clean edges.

Common sources of variation include:

GSM and thickness should be reviewed together. If thickness is within specification but GSM is high, the film may contain a higher-density polymer, coating, adhesive, filler, or ink load. If both GSM and thickness vary, the extrusion process may require adjustment.

What Is GSM in Packaging?

GSM in packaging is the mass of one square meter of material, expressed in grams. It is commonly used for paper, cardboard, nonwoven materials, and plastic film. In packaging film, GSM helps you estimate material usage and verify whether the film matches the agreed specification.

For plastic film, GSM is influenced by thickness, density, and the composition of the film. A 25-micron PET film will weigh more per square meter than a 25-micron polyethylene film because PET has a higher density.

Why GSM Matters in Film Production

GSM provides a practical way to monitor material consumption and production consistency. A film roll that is heavier than expected may contain excess material, while a roll that is too light may have insufficient thickness or an incorrect layer ratio.

GSM is used for:

GSM is not the same as strength. A higher GSM can indicate more material, but strength also depends on polymer type, molecular structure, orientation, additives, layer design, and processing conditions.

For example, an oriented BOPP film may have a lower GSM than a thicker polyethylene film but still provide high tensile strength and good stiffness. You should use GSM alongside tensile testing, seal testing, and barrier testing when selecting packaging film.

Common GSM Ranges in Packaging Film

There is no single GSM range for all packaging film. The correct value depends on the application, film type, package size, sealing method, and required protection.

*Approximate values depend on resin density, coatings, inks, adhesives, and laminate structure.

Differences Between Different Types of Packaging Film

Packaging films differ in material composition, thickness, orientation, barrier performance, strength, appearance, sealing behavior, and end use. You should select the film according to the product and packaging process rather than choosing a material based only on price or appearance.

A film that works well for dry snacks may not be suitable for fresh produce. Similarly, a clear film used for retail visibility may not provide enough oxygen or light protection for a sensitive pharmaceutical or food product.

Polyethylene Film

Polyethylene film is flexible, lightweight, and resistant to moisture. It is one of the most widely used materials for bags, liners, pouches, stretch film, shrink film, and overwrap.

LDPE provides good flexibility and sealing performance. LLDPE is often used when you need greater puncture resistance and tensile strength. HDPE offers more stiffness and a crisper feel.

Polyethylene generally provides a good moisture barrier but a weaker oxygen barrier than materials such as PET, EVOH, or aluminum foil. For products sensitive to oxygen, polyethylene is often used as the inner sealant layer in a multilayer structure rather than as the only film.

Polypropylene Film

Polypropylene film provides good stiffness, clarity, heat resistance, and chemical resistance. It is used in food packaging, pharmaceutical packaging, labels, tape, and consumer product packaging.

BOPP film is stretched in the machine direction and transverse direction. This biaxial orientation improves tensile strength, optical clarity, gloss, and dimensional stability. BOPP is widely used for snack packs, confectionery packaging, labels, and printed wrap.

Polypropylene can be difficult to heat-seal unless it has a suitable sealant layer or coating. Packaging equipment settings must be matched to the specific PP grade and film construction.

Polyvinyl Chloride Film

PVC film can be manufactured as either a flexible or rigid material. It offers good clarity, impact resistance, and dimensional stability in selected applications.

PVC is used for clamshell packaging, shrink sleeves, blister packaging, and other specialty formats. Its suitability depends on the formulation, plasticizer system, product-contact requirements, and local regulations.

When choosing PVC, you should review the application carefully. Regulations and customer policies may restrict certain PVC formulations, additives, or disposal routes.

Polyester Film

PET film is strong, dimensionally stable, and resistant to heat and many chemicals. It has good clarity and provides a reliable surface for printing, coating, and metallization.

PET is commonly used as the outer layer of laminated pouches for coffee, snacks, medical products, electronics, and industrial goods. It contributes strength and print performance but is not usually the primary heat-sealing layer.

Its higher density means that PET film has a higher GSM than a polyethylene or polypropylene film at the same thickness.

Biaxially Oriented Polypropylene Film

BOPP film combines low density with high tensile strength, clarity, gloss, and moisture resistance. It can be treated for printing, coated for heat sealing, or metallized to improve light and gas barrier performance.

You will often see BOPP in snack packaging, candy wrappers, labels, pressure-sensitive tape, and bakery packaging. Its low moisture absorption and attractive appearance make it suitable for high-speed consumer packaging lines.

BOPP is not automatically appropriate for every application. You should evaluate its seal initiation temperature, coefficient of friction, stiffness, and barrier performance against the requirements of the packaging machine and product.

Biodegradable and Compostable Films

Biodegradable and compostable films may be made from materials such as PLA, PHA, starch blends, or other bio-based polymers. Their environmental performance depends on the polymer, additives, thickness, coating, printing system, and disposal conditions.

A compostable film does not necessarily break down in ordinary soil, marine environments, or a household compost pile. Many products require controlled industrial composting conditions. You should verify the relevant certification and disposal infrastructure before making an environmental claim.

These films can be suitable for selected produce, bakery, food-service, and consumer packaging applications. Their moisture barrier, oxygen barrier, heat resistance, sealing window, and shelf-life performance must be tested for the specific product.

Key Differences Between Packaging Films

Material Composition

The polymer determines the basic behavior of the film. PE is usually selected for flexibility and sealing. PP is used for stiffness and clarity. PET provides strength and heat resistance. PVC serves selected rigid and flexible applications, while biodegradable polymers are considered where a verified end-of-life route exists.

Multilayer films combine these materials to meet several requirements at once. For example, a pouch may use PET for printing and stiffness, aluminum or metallization for light and oxygen protection, and PE for sealing.

Barrier Properties

Barrier properties describe how well the film limits the passage of moisture, oxygen, carbon dioxide, aromas, light, and other substances.

Actual barrier performance depends on thickness, temperature, humidity, orientation, coating quality, and laminate design. You should use measured oxygen transmission rate and water vapor transmission rate data when shelf life is critical.

Strength and Durability

Film strength is evaluated through tensile strength, elongation, tear resistance, puncture resistance, impact resistance, and seal strength. These properties determine whether the package can survive filling, stacking, transport, and consumer handling.

A high-strength outer film may reduce package failures without requiring a very thick structure. Orientation can also improve tensile properties, although oriented films may have different tear behavior in different directions.

For heavy or sharp products, puncture resistance can be more important than clarity. For automatic packaging equipment, coefficient of friction, stiffness, and web stability may be more important than maximum tensile strength.

Clarity and Aesthetic Appeal

Clarity, haze, gloss, surface smoothness, and print quality influence how the product appears at the point of sale. Clear film is useful when you want customers to see the product. Opaque, white, metallized, or printed film is used when you need light protection or a specific visual effect.

Surface treatment affects ink adhesion and coating performance. If the film will be printed, laminated, or coated, the supplier should provide information about treatment level and surface energy.

Environmental Considerations

Environmental assessment should include the complete packaging system, not only whether a film is described as recyclable or biodegradable. Material reduction, recycled content, production energy, transport weight, package performance, and end-of-life infrastructure all affect the result.

A thinner film that fails during transport can create more product waste and may not deliver a better overall outcome. You should balance downgauging with seal strength, puncture resistance, shelf life, and machine performance.

Where recycling is available, mono-material PE or PP structures may be easier to sort and process than complex laminates. However, local collection and recycling systems determine whether the material is actually recovered.

Cost and Customization

PE and PP films are often cost-effective for high-volume applications. PET, metallized films, barrier coatings, specialty sealants, and multilayer structures can increase cost but may provide longer shelf life or better product protection.

Your total packaging cost includes more than the film price. Consider:

1. Film weight and material usage
2. Printing and lamination costs
3. Packaging machine speed
4. Product loss caused by weak packaging
5. Storage and transport efficiency
6. Roll yield and waste
7. Required testing and compliance documentation

How to Choose the Right Packaging Film

Choosing the right packaging film requires you to match the film structure to the product, packaging machine, distribution environment, and end-of-life requirements. Start with the product’s sensitivity and handling risks, then confirm the film’s barrier, mechanical, sealing, and regulatory performance.

Consider the Product Type and Its Requirements

The product determines the first set of film requirements. Fresh produce may need ventilation or controlled gas transmission. Dry snacks may need strong moisture and oxygen protection. Pharmaceutical packaging may require tamper evidence, sterility protection, and documented compliance.

You should also consider whether the product is sharp, oily, powdered, liquid, fragile, or temperature-sensitive. The film must withstand contact with the product without losing seal strength, clarity, or barrier performance.

Evaluate Barrier Properties

Ask which external factors can reduce product quality. Moisture can soften dry foods or damage powders. Oxygen can cause oxidation, flavor loss, color changes, or nutrient degradation. Light can affect food, cosmetics, and pharmaceutical products.

Barrier performance should be based on test data rather than general material descriptions. Important measurements include oxygen transmission rate, water vapor transmission rate, aroma transmission, light transmission, and seal integrity after storage.

Temperature and humidity also matter. A film can perform differently in a cold warehouse, hot truck, refrigerated display, or high-humidity environment.

Consider Strength and Durability

The film must survive the entire supply chain. Evaluate how the package will be filled, sealed, stacked, palletized, transported, opened, and handled by the consumer.

Important mechanical questions include:

A thicker film is not always the best solution. A properly oriented or laminated structure may provide better performance at a lower total GSM.

Assess Aesthetic and Branding Needs

Film can support brand presentation through transparency, gloss, matte effects, metallic appearance, color, texture, and high-resolution printing.

For retail products, consider whether the customer needs to see the contents. Clear film may improve product visibility, while opaque or metallized film can protect light-sensitive contents and create a stronger visual contrast.

You should also specify the printing method, number of colors, print side, ink system, barcode requirements, and resistance to rubbing or condensation. The film surface must be compatible with the selected ink and any later coating or lamination process.

Consider Sustainability and Environmental Impact

Sustainability decisions should be based on verified claims and the available waste-management system. Review whether the selected structure is accepted by local recycling programs and whether coatings, adhesives, inks, or metallization affect recyclability.

Material reduction can lower packaging weight, but it should be supported by performance testing. A downgauged film must still meet seal strength, puncture resistance, barrier, and transport requirements.

For biodegradable or compostable films, verify:

Balance Cost and Performance

The right film provides the required protection at the lowest practical total cost. A low-cost film may become more expensive if it reduces machine speed, increases rejects, causes seal failures, or shortens product shelf life.

Compare suppliers using the same technical requirements. Your specification should identify resin type, film thickness, GSM range, width, roll length, core size, winding direction, surface treatment, coefficient of friction, seal strength, and required barrier values.

For multilayer film, request the full layer structure and tolerance for each layer. This makes it easier to compare suppliers and identify changes that could affect packaging performance. You should approve the final material only after testing it on the actual packaging machine and, where necessary, conducting product shelf-life trials.