Understanding the Difference: Heat-sealable vs. Non-Sealable Metallized BOPP

In the world of flexible packaging, the choice of material is a critical determinant of a product’s protection, shelf appeal, and manufacturing efficiency. Among the most versatile and widely used materials are metallized films, prized for their excellent barrier properties and brilliant aesthetic. However, a fundamental and often overlooked distinction lies at the heart of selecting the right film: whether it is heat-sealable or non-sealable. This decision directly impacts the entire packaging process, the final package structure, and ultimately, the product’s success in the market.

The term bopp film stands for Biaxially Oriented Polypropylene, a substrate known for its clarity, strength, and moisture resistance. The metallization process, which involves depositing a thin layer of aluminum onto the film in a vacuum chamber, enhances these properties by adding a superior barrier to light, oxygen, and moisture, along with a distinctive metallic sheen. The pivotal difference emerges in the final layer of the film’s structure, which dictates its sealing capabilities. Understanding this distinction is not merely a technical exercise; it is a crucial business decision that influences production line speed, packaging integrity, and material costs.

The Fundamental Distinction: A Matter of Sealing Capability

At its most basic level, the difference between these two films can be summarized in a single sentence: a heat-sealable metallized BOPP film possesses a dedicated sealing layer that allows it to bond to itself or other surfaces under heat and pressure, while a non-sealable metallized BOPP film lacks this layer and cannot form such a seal. This seemingly simple disparity has profound implications for how each film is used in packaging construction.

A non-sealable metallized BOPP film is essentially a monolithic functional and aesthetic layer. It is designed to provide a barrier and appearance but must rely on another material to form the seals of a package. Think of it as a beautiful and strong wall panel; it serves a vital purpose, but it cannot create the joints or corners of a structure on its own. In contrast, a heat-sealable metallized bopp film is a multi-functional, co-extruded material. It combines the barrier and aesthetics of the metallized base layer with the sealing functionality of a specialized polymer coating. This makes it an all-in-one solution that can form the sealed seams of a package, acting as both the wall and the mortar.

This core distinction dictates their entire value proposition. The selection process begins by asking one fundamental question: Will this film be used to form the primary seal of the package? If the answer is yes, then a heat-sealable metallized bopp film is the necessary and only logical choice. If the answer is no, and the film will be used in a laminated structure where another material provides the seal, then the non-sealable variant may be a more economical and appropriate option.

Deep Dive into Heat-sealable Metallized BOPP Film

Structure and Composition

A heat-sealable metallized bopp film is a sophisticated, multi-layer material engineered for performance. Its structure is typically the result of co-extrusion, a process where multiple layers of polymer are combined during the film manufacturing stage.

The core of the film is the bopp substrate. This base layer provides the film with its mechanical strength, dimensional stability, and inherent moisture barrier. It is biaxially oriented, meaning it is stretched in both the machine and transverse directions, which aligns the polymer molecules and significantly enhances its tensile strength, clarity, and gas barrier properties. Upon this robust base, an ultra-thin layer of aluminum is deposited in a vacuum chamber. This metallization process is what gives the film its characteristic shiny, metallic appearance and, more importantly, dramatically improves its barrier against oxygen, light, and aromas.

The critical differentiator, however, is the sealant layer. This is a specialized polymer coating, often a variant of polypropylene (PP) or polyethylene (PE), applied to one side of the metallized film. This layer has a lower melting point than the BOPP core. When heat and pressure are applied through sealing jaws, this sealant layer melts and flows, creating a molecular bond with the opposing surface—whether it is another section of the same film or a compatible sealant layer on a different material. The integrity of this seal is paramount, as it is the primary defense against contamination and spoilage for the packaged product.

Key Functional Mechanisms

The functionality of heat-sealable metallized bopp film hinges on the performance of its sealant layer. The primary mechanism is thermal sealing. The film is fed through a packaging machine where heated jaws press against it along the intended seal areas. The heat is precisely controlled to melt the sealant layer without damaging the BOPP core or the metallized layer. The applied pressure ensures intimate contact and allows the molten polymer to fuse, creating a hermetic seal upon cooling. Key performance indicators for this process include seal initiation temperature, seal strength, and hot tack strength.

Hot tack strength is a particularly crucial property. It refers to the strength of the seal while it is still hot and directly after the jaws release, but before it has fully cooled and crystallized. A film with high hot tack strength allows packaging machines to run at higher speeds because the sealed packages can be handled and filled more aggressively without the seals pulling apart. This is a critical consideration for high-speed packaging lines for snacks and other fast-moving consumer goods. The barrier properties of the film are a function of the combined BOPP substrate and the metallization layer. The sealed seams, once formed, must maintain this barrier, making the uniformity and integrity of the seal as important as the bulk barrier properties of the film itself.

Primary Applications and Advantages

The all-in-one nature of heat-sealable metallized bopp film makes it the material of choice for a wide range of flexible packaging applications where it serves as the sole material or the inner layer of a simple laminate.

Common applications include:

• Stand-up pouches for snacks like chips and nuts, where the film provides the barrier, aesthetics, and the seals that create the pouch’s gussets and top.
• Flow wraps and pillow packs for candy, confectionery, and baked goods.
• Lidding film for cups and trays, where the film seals directly onto the rigid plastic rim.
• Packaging for dehydrated soups and other powder-based foods that require a strong moisture barrier.

The advantages are significant:

• Simplified Packaging Structure: It often functions as a single-web material, eliminating the need and cost of a separate lamination process.
• High Production Efficiency: Its excellent machinability and hot tack strength enable faster filling and sealing on vertical form-fill-seal (VFFS) and horizontal form-fill-seal (HFFS) equipment.
• Superior Package Integrity: The consistent, hermetic seals ensure product freshness and prevent leakage.
• Excellent Consumer Appeal: The high-gloss, metallic finish is highly effective at attracting attention on retail shelves.

Exploring Non-Sealable Metallized BOPP Film

Structure and Composition

Non-sealable metallized BOPP film has a simpler, two-component structure. It consists of the biaxially oriented polypropylene base film and the vacuum-deposited metallized layer. Crucially, it lacks any form of heat-sealable coating. The surface of the film, typically the non-metallized side, is often treated via corona discharge or other methods to increase its surface energy. This treatment makes the surface more receptive to inks and adhesives, which is essential for its primary function: to be a component in a larger laminated structure.

In this film, the metallized layer is the primary functional layer. Its purpose is to provide the maximum possible barrier to gases and light. Since no sealing layer is required, the BOPP substrate can be optimized purely for its mechanical and barrier properties, and the metallization process can be fine-tuned to achieve a specific optical density and barrier level without concern for how it might affect a sealant layer. The film is, in essence, a high-performance, decorative barrier web that is designed to be combined with other materials.

Key Functional Mechanisms

The functionality of non-sealable metallized BOPP is passive rather than active. It does not form seals; it provides a barrier and a surface for printing. Its primary mechanism is as a component in a lamination. It is combined with other films or materials using adhesives in a process called adhesive lamination or via extrusion lamination, where a molten polymer is used as the bonding agent.

In a typical laminate structure, the non-sealable metallized BOPP serves as the outer or middle ply. Its high-gloss surface provides an excellent substrate for high-quality rotogravure printing, allowing for vibrant and sharp graphics. The metallized layer, buried within the laminate, is protected from abrasion and cracking, which helps maintain the barrier integrity of the final package. The sealing function is provided by the innermost layer of the laminate, which is a sealant film like cast polypropylene (CPP) or polyethylene (PE). This separation of duties allows each layer to be optimized for its specific role: the outer for graphics and toughness, the middle for barrier, and the inner for sealing.

Primary Applications and Advantages

Non-sealable metallized BOPP film finds its niche in complex, high-performance packaging structures that require a combination of properties no single film can provide.

Common applications include:

• Laminated pouches for products requiring very high barrier properties, such as coffee, processed meats, and premium snacks.
• Liquid packaging where the laminate structure provides strength, barrier, and seal integrity against liquids.
• Pharmaceutical blister lidding where the film provides a barrier and is laminated to a foil for puncture resistance and peelability.
• As an outer layer in gift wraps and decorative labels.

The advantages of this film are rooted in its specialized role:

• Optimized Barrier and Graphics: By decoupling the barrier layer from the sealing layer, both can be maximized for performance. The film can be heavily metallized for an ultra-high barrier without affecting sealability.
• Design Flexibility: It allows packaging engineers to create custom laminates by combining the best attributes of several materials (e.g., PET for stiffness, metallized BOPP for barrier, and CPP for sealing).
• Cost-Effectiveness in Complex Structures: For packages that require multiple layers anyway, using a non-sealable film can be more economical than using a more expensive heat-sealable version that provides unnecessary functionality.
• Superior Printability: The treated surface is ideal for high-end printing, resulting in exceptional graphic quality.

Head-to-Head Comparison: A Detailed Analysis

To make an informed decision, a side-by-side comparison of key parameters is essential. The following table and analysis highlight the critical differences.

Analysis of Key Differentiators

1. Packaging Line Implications: The choice of film dictates the type of packaging machinery required. A heat-sealable metallized bopp film is designed for direct use on form-fill-seal equipment. Its selection is driven by the need for operational efficiency and a streamlined supply chain. Conversely, non-sealable film must first be sent to a converter to be laminated with a sealant web. This adds a processing step but results in a rollstock material that offers performance characteristics unattainable with a single film.

2. Barrier Performance and Integrity: While both films offer good barrier properties, the approach is different. For the heat-sealable type, the overall package barrier is a function of the film’s bulk barrier and the integrity of the heat seals. Any weakness or inconsistency in the seal becomes a critical failure point. For the non-sealable type used in a laminate, the barrier is provided by the metallized layer, which is protected within the structure. The seal integrity is the responsibility of the inner sealant layer, which is specialized for that task. This can lead to a more robust and reliable barrier system for demanding products.

3. Economic and Supply Chain Considerations: The decision is not solely about the cost per square meter of the film. For a packaging buyer, the total cost of ownership must be considered. Using a heat-sealable metallized bopp film can reduce costs by minimizing conversion steps (e.g., no lamination) and increasing line speeds. However, for a product that requires the superior barrier and graphic appeal of a complex laminate, attempting to use a heat-sealable film as a substitute would be counterproductive and could lead to product failure. In such cases, the laminated structure using non-sealable film, despite its higher initial material cost, provides better value by ensuring product quality and shelf life.

How to Make the Right Choice for Your Application

Selecting between these two films is a strategic decision that should be based on a clear assessment of the product’s needs, the packaging process, and the market requirements.

Choose Heat-sealable Metallized BOPP Film when:

• The packaging operation uses vertical form-fill-seal or horizontal form-fill-seal equipment.
• The primary requirement is for a moisture barrier and aroma barrier for dry products.
• Production speed and operational simplicity are key drivers.
• The package structure is simple, such as a pillow pack or a stand-up pouch without complex features.
• The product is cost-sensitive and the packaging structure must be minimized.

Choose Non-Sealable Metallized BOPP Film when:

• The packaged product demands an ultra-high barrier to oxygen or requires a long shelf life.
• The package is a liquid or contains oils and fats that necessitate a robust laminate structure.
• The highest quality of printing and graphic appeal is a top priority for brand differentiation.
• The packaging structure is inherently multi-ply, and the film’s role is specifically to provide a protected barrier layer and print surface.
• The package format is a pre-made pouch or requires lidding to a rigid container.

The most critical step in the selection process is a thorough needs analysis. Engaging with material suppliers and packaging engineers early on to discuss the product characteristics, distribution environment, and marketing goals will lead to the optimal and most cost-effective choice. It is a balance of performance, process, and price, where understanding the fundamental difference between sealing and non-sealing is the first and most important step.

The distinction between heat-sealable metallized bopp film and non-sealable metallized BOPP is a fundamental one, rooted in their core structure and functional purpose. The former is an integrated, active packaging material capable of forming the sealed confines of a package, offering efficiency and simplicity for a wide range of applications. The latter is a specialized, passive component that provides superior barrier and graphic potential as part of a engineered laminate, delivering performance for demanding products. There is no universal “better” option; there is only the right tool for the job. For packaging professionals, buyers, and wholesalers, a deep understanding of this difference is not just technical knowledge—it is a crucial element of strategic sourcing, product development, and ensuring that the final package reliably protects the product, appeals to the consumer, and is produced in the most efficient manner possible. By carefully considering the requirements outlined in this article, one can navigate this critical material selection with confidence and clarity.