Walk into any supermarket and pick up a bag of potato chips. The shiny inner surface that keeps the chips crisp and the sunlight out — that is a metallized film. Now walk over to the coffee aisle and look at a foil-laminated stand-up pouch. Different product, different look, but also a metallized film inside. Both packages rely on a sub-micron layer of aluminum deposited onto a plastic substrate. But the substrate itself — the plastic film that carries the aluminum — is where the critical differences hide.
The two most common substrates for metallization are PET (polyethylene terephthalate) and BOPP (biaxially oriented polypropylene). They look similar on a specification sheet. They do not perform the same way in a packaging line or on a shelf. Choosing the wrong one can mean seal failures, barrier breakdown, print registration drift, or a package that simply does not look premium enough for its price point.
This article compares PET and BOPP metallized films across the criteria that matter most: thermal behavior, barrier performance, mechanical stiffness, optical appearance, converting compatibility, and cost. By the end, you will know which substrate belongs in your package — and why.
The Substrate Differences Start Before the Aluminum
Before any aluminum enters the vacuum chamber, PET and BOPP are fundamentally different materials. PET is a polyester, synthesized from ethylene glycol and terephthalic acid. Its molecular chain contains rigid aromatic rings that give the polymer its characteristic stiffness, heat resistance, and excellent oxygen barrier — even before metallization.
BOPP is polypropylene that has been stretched in two directions (machine and transverse) to align its molecular chains. This biaxial orientation gives BOPP its clarity, flexibility, and moisture barrier. But polypropylene has a lower melting point than PET and a more open molecular structure, which means its inherent oxygen barrier — before any aluminum is added — is relatively poor.
These baseline differences cascade into every performance metric after metallization. The aluminum layer enhances both films, but it cannot erase the characteristics of the polymer underneath.
Thermal Resistance: The Deciding Factor for Hot Applications
This is where PET and BOPP diverge most dramatically. PET has a melting point of approximately 260°C (500°F) and a continuous service temperature exceeding 150°C (300°F). BOPP melts at approximately 160°C (320°F) and begins to soften well below that.
What does this mean in practice? If your packaging process involves hot-fill liquids (sauces, soups, ready-to-drink beverages), retort sterilization, or microwave reheating, PET metallized film handles the heat without dimensional change. BOPP metallized film will shrink, distort, or even melt under the same conditions.
For cold-fill and ambient-temperature applications — snack foods, dry goods, confectionery — BOPP performs perfectly well and costs less. The thermal requirement of your process is the first filter: if heat is involved, PET is almost always the answer.
>> Rule of thumb: If your packaging line exceeds 80°C (176°F) at any point — filling, sealing, retorting, or end-use reheating — choose PET metallized film over BOPP.
Barrier Performance: Oxygen, Moisture, and Light
Both PET and BOPP achieve dramatic barrier improvements after metallization. A thin layer of vacuum-deposited aluminum — typically 300 to 500 angstroms thick — reduces oxygen transmission rates (OTR) from thousands of cc/m²/day to below 1 cc/m²/day, and water vapor transmission rates (WVTR) from several g/m²/day to below 0.5 g/m²/day.
But the starting point matters. PET already has a naturally lower OTR than BOPP before metallization. After metallization, both films can achieve similar barrier numbers when the aluminum layer is intact and uniform. The difference emerges when the package is flexed, folded, or stressed during distribution. PET’s higher stiffness reduces micro-cracking of the aluminum layer under mechanical stress, preserving barrier integrity better than the more flexible BOPP substrate.
For light barrier (opacity), both metallized films are effectively opaque at standard aluminum deposition thicknesses. Optical density values of 2.0 to 3.0 are achievable on both substrates, providing excellent UV and visible light protection for light-sensitive products like coffee, nuts, and pharmaceuticals.
Stiffness, Handling, and Converting
PET metallized film is stiffer and has higher tensile strength than BOPP metallized film of the same gauge. This stiffness is an advantage in certain converting operations: die-cutting for lidding films, maintaining flatness during printing registration, and resisting wrinkle formation during lamination. PET film lays flat and stays flat.
However, stiffness can also be a limitation. PET is less conformable around irregular shapes. For flow-wrap applications where the film must hug the product tightly, BOPP’s flexibility and dead-fold characteristics may be preferable.
On the converting line, both films are compatible with gravure and flexographic printing, but PET’s dimensional stability at elevated drying temperatures gives it an edge in high-speed printing where registration accuracy is critical. BOPP can stretch or distort under the heat of drying tunnels if tension control is not precise.
Optical Appearance: The Premium Look
PET metallized film typically produces a brighter, higher-reflectivity surface than BOPP metallized film. This is partly due to PET’s inherently smoother surface, which allows the aluminum layer to deposit more uniformly. The result is a mirror-like finish that signals “premium” to the consumer.
BOPP metallized film can achieve good reflectivity, but the naturally more irregular surface of oriented polypropylene creates slightly more light scatter. For applications where shelf appeal and visual impact are paramount — gift wrap, premium confectionery, high-end personal care — PET metallized film delivers a more striking appearance.
Cost: Where BOPP Wins
On a per-kilogram basis, BOPP resin is generally less expensive than PET resin. The metallization process cost is similar for both substrates. As a result, BOPP metallized film typically has a lower unit cost than PET metallized film of equivalent gauge.
For high-volume, cost-sensitive applications where thermal resistance is not required — snack packaging, confectionery, dry food pouches — BOPP metallized film is often the economical choice. PET metallized film commands its premium through performance: it earns its place in applications where BOPP simply cannot deliver.
Quick Decision Guide
Use this summary to guide your selection:
Frequently Asked Questions
Q: Can PET and BOPP metallized films be laminated together?
Yes. A common structure for high-barrier flexible packaging is PET-met / adhesive / PE sealant. The PET layer provides stiffness, thermal resistance, and barrier; the PE layer provides heat-sealability. BOPP-met can be used in similar laminates where thermal requirements are lower.
Q: Which metallized film is better for retort pouches?
PET metallized film is the clear choice for retort applications. BOPP cannot withstand retort temperatures (typically 121°C to 135°C). PET-met maintains its barrier properties and dimensional integrity through the retort cycle.
Q: Can I print directly on the metal side of PET metallized film?
Yes, but it requires a primer or top-coat to ensure ink adhesion to the aluminum surface. The non-metal side of PET film accepts ink well with standard corona treatment.
Q: Is PET metallized film recyclable?
Metallized PET film is technically recyclable in PET recycling streams, though the aluminum layer (which is extremely thin) may require separation. The aluminum content is typically less than 0.1% by weight, so it does not significantly impact the recycled PET quality. Metallized BOPP faces similar considerations in PP streams.
Q: Which film has better metal adhesion?
PET generally provides better metal adhesion than BOPP because its surface is more polar and receptive to the aluminum vapor during deposition. This translates to better barrier retention after flexing and handling.
About the Author
Shandong Shunzhan New Materials Co., Ltd. is a professional manufacturer of metallized BOPP and PET films, serving packaging converters and brand owners in over 30 countries. Our team combines deep materials science knowledge with practical converting experience to help clients select the right metallized film for their specific application. Need technical guidance on PET metallized film? Contact us at mia@szbopp.com or visit szbopp.com for a free consultation — no purchase necessary.
PET镀铝膜 vs. BOPP镀铝膜：哪种该进你的包装袋？
走进任何一家超市，拿起一袋薯片。让薯片保持酥脆、隔绝阳光的那层闪亮内表面——那就是镀铝膜。再走到咖啡货架，看一眼铝箔复合的直立袋。不同产品，不同外观，但里面也是镀铝膜。两种包装都依赖在塑料基材上沉积的亚微米铝层。但基材本身——承载铝层的那层塑料薄膜——才是关键差异隐藏的地方。
两种最常见的镀铝基材是PET（聚对苯二甲酸乙二醇酯）和BOPP（双向拉伸聚丙烯）。它们在规格单上看起来很相似，但在包装线上或货架上的表现却截然不同。选错基材可能导致封口失败、阻隔性能崩溃、印刷套准漂移，或者包装看起来根本配不上它的价格定位。
本文从热性能、阻隔性能、机械刚性、光学外观、加工兼容性和成本等关键维度对比PET和BOPP镀铝膜。读完你将清楚哪种基材应该进入你的包装——以及为什么。
基材差异：铝层到来之前就已存在
在任何铝进入真空室之前，PET和BOPP就是根本不同的材料。PET是一种聚酯，由乙二醇和对苯二甲酸合成。其分子链含有刚性的芳香环，赋予聚合物特有的刚性、耐热性和优异的氧气阻隔性——甚至在镀铝之前就已具备。BOPP是经过双向拉伸（纵向和横向）使其分子链排列的聚丙烯。这种双向拉伸赋予BOPP透明度、柔韧性和水蒸气阻隔性。但聚丙烯的熔点低于PET，分子结构更加开放，这意味着其在镀铝之前的固有氧气阻隔性相对较差。
这些基线差异会层层传导到镀铝后的每一个性能指标中。铝层增强了两者，但无法抹去底层聚合物的特性。
耐热性：高温应用的决定因素
这是PET和BOPP差异最显著的地方。PET的熔点约为260°C，连续使用温度超过150°C。BOPP的熔点约为160°C，远在此之前就开始软化。在实践中这意味着什么？如果你的包装工艺涉及热灌装液体（酱料、汤品、即饮饮料）、蒸煮灭菌或微波复热，PET镀铝膜可以在高温下不发生尺寸变化。BOPP镀铝膜在相同条件下会收缩、变形甚至熔化。
对于冷灌装和常温应用——休闲食品、干货、糖果——BOPP表现完美且成本更低。工艺的耐热需求是第一道筛子：如果涉及热量，PET几乎总是答案。
阻隔性能：氧气、水蒸气和光线
PET和BOPP在镀铝后都能实现阻隔性能的显著提升。一层真空沉积的薄铝层——通常300到500埃厚——将氧气透过率（OTR）从数千cc/m²/day降至不到1 cc/m²/day，水蒸气透过率（WVTR）从数g/m²/day降至不到0.5 g/m²/day。
但起点很重要。PET在镀铝前天然具有比BOPP更低的OTR。镀铝后，当铝层完整均匀时，两者可以达到相近的阻隔数值。差异在包装在分销过程中受到弯折、折叠或应力时显现：PET更高的刚性减少了铝层在机械应力下的微裂纹，比更柔软的BOPP基材更好地保持了阻隔完整性。
刚性、操作和加工
PET镀铝膜比相同厚度的BOPP镀铝膜更刚硬，抗拉强度更高。这种刚性在某些加工工序中是优势：盖膜模切、印刷套准中保持平整、复合过程中抵抗起皱。PET薄膜铺得平，保持得平。然而，刚性也可能成为局限。PET在不规则形状周围的贴合性较差。对于需要薄膜紧密包裹产品的流动包装，BOPP的柔韧性和死折特性可能更合适。
光学外观：高级感
PET镀铝膜通常比BOPP镀铝膜产生更亮、反射率更高的表面。部分原因是PET天然更光滑的表面使铝层沉积更均匀。结果是镜面般的表面效果，向消费者传递“高端”的信号。BOPP镀铝膜可以做到不错的反射率，但取向聚丙烯天然更不规则的表面会产生稍多的光散射。对于货架吸引力和视觉冲击力至关重要的应用——礼品包装、高端糖果、高级个人护理品——PET镀铝膜呈现更惊艳的外观。
成本：BOPP的优势所在
按公斤计算，BOPP树脂通常比PET树脂便宜。两种基材的镀铝工艺成本相近。因此，BOPP镀铝膜的单位成本通常低于同等厚度的PET镀铝膜。对于高产量、成本敏感且不要求耐热的应用——零食包装、糖果、干货袋——BOPP镀铝膜往往是经济选择。PET镀铝膜通过性能赢得其溢价：它在BOPP根本无法胜任的应用中证明了自身价值。
About the Author
Shandong Shunzhan New Materials Co., Ltd. is a professional manufacturer of metallized BOPP and PET films, serving packaging converters and brand owners in over 30 countries. Our team combines deep materials science knowledge with practical converting experience to help clients select the right metallized film for their specific application. Need technical guidance on PET metallized film? Contact us at mia@szbopp.com or visit szbopp.com for a free consultation — no purchase necessary.