Aluminum foil and metallized PET-Film (PET-met): Applications & Differences

Reel of golden PET-met

Aluminium foil has been used for more than 100 years especially in the packaging industry. But meanwhile a serious competitor has entered the arena. Metallized PET films cover an ever-growing range of applications, making it one of the fastest growing segments in the flexible packaging market.

At first sight, the two types of films are similar. However, they offer very different properties, making each of them more or worse suitable depending on the applications.

Properties of aluminum foil

Aluminium foil is usually made of pure aluminium, with an aluminium content of at least 99%. In a series of passes through rolling mills the aluminium reaches the desired thickness.

Very thin foils are double-rolled together in the last step and later, separated again This process produce two kind of natural finishes: the outer side of the foil touching the mill work rolls gets a “bright” finish, while the side contacting the other aluminium foil (foil-to-foil) gets a “matte” finish.

The aluminium is solidified by the cold rolling, becoming hard and brittle. Nevertheless, a subsequent thermal treatment in an annealing furnace makes the films soft and flexible again.

Food packaging made of Aluminium

Chocolate wrapping made of Aluminium foil

Aluminium foils with a thickness of about 12-20 µ possess  barrier properties. This means that those foils are impermeable to water and gases. Thinner foils cannot guarantee the same 100% barrier properties. However, they also offer barrier properties and ensure that food stays fresh longer because of its light protection.

Aluminium foil is easily deformable without losing its barrier properties.

Due to its natural, protective and rust-resistant shield on the surface, aluminium foil is physiologically harmless to food and it has a passive behaviour in aqueous solutions. However, the solubility of this protective layer increases in acidic and alkaline media. Consequently, acidic, alkaline or salty food should not be packed in aluminium foil.

Aluminium coffee capsules

Coffee capsules are also made of Aluminium

This foil is light and resistant to water, water vapor, grease and gas. It reflects light, heat and UV rays. Moreover, it is fire-resistant and easily recyclable. Aluminium strips can be deep-drawn to produce cans and so-called semi-rigid containers, e.g. barbecue trays; these cans and containers keep their form. Aluminium foil can be bent without losing the barrier properties or protective characteristics. For certain applications, the aluminium is laminated with paper and/or plastic films, such as PE, PET or PP, thus adding more advantages to the already listed properties. And those, in turn, could be painted and printed.

Properties of PET-met film

In contrast to aluminium foil, which is made completely of the light metal, metallized PET-films are only evaporated with aluminium powder in a high vacuum. For this process, it is used pure aluminium in powder form with an aluminium content of at least 99,98%. The films produced this way obtain a metallic shine, which is generally glossier than aluminium foils. In the industry, metallized PET films are often called “PET-met foils” or “PET-met films”.

The metallization of the PET-film serves in particular to improve its barrier effect against vapours, gases and aromas, but also for decorative purposes. All metallized PET-films are less gas-tight, but they are more tear resistant, more flexible, lighter and not as winkle-prone as pure aluminium foil. As a plastic film, it is less sensitive to corrosion.

You cannot see through aluminium foil,

but you can in general see through PET met film.

Aluminium pouches and PET-met pouches

Pouches made of aluminum and metallized PET film (PET-met). The shining bags are made of PET-met.

PET-met films are made of only 1% of the aluminium that an aluminium foil would have been made of. This implies that the barrier properties of metallized film are weaker than those of classic aluminium foil. Nonetheless, PET-met films are a more economic and an environmentally friendly substitute for classic aluminium, in the case that the stronger protective properties of aluminium film are not required for the application.

Applications for aluminum foil

Aluminium foils are true all-rounder, which can be found in almost all sectors of the industry. Light and yet tear-resistant, it can be folded in many ways making it ideally suited for packing and wrapping different kind of products and shapes. In the pharmaceutical industry, aluminium film is used to protect drugs from external influences during transport and storage. The food industry relies on packaging made of aluminium foil and laminated aluminium films, thereby benefiting from the good hygienic characteristics and the light and gas barrier properties of the material. A large number of aluminium tubes and aerosol cans are used in the cosmetics industry.

In the construction industry, the insulating attributes of aluminium foil are most important, e.g. for insulating cable ducts, water pipes and whole buildings, as well as the construction of vapour barriers for saunas or on cellar walls. In the energy sector, the low weight and the high conductivity of the aluminium foil are particularly important when insulating power cables. The telecommunication industry, on the other hand, uses its special barrier properties to protect fibre optic cables from humidity and shield electrostatic interference by electronic devices.

Applications for metallized PET-film

Metallized PET films are an ideal solution for all applications that require the preservation of flavour and freshness. It is suitable for many applications in the packaging industry as well as for technical and industrial applications. PET-met foils offer advantages in particular where the higher gas tightness of the aluminum foil is not required.

The metallized PET film is available in a variety of optical variants. That is why they are the ideal material to combine protection and barrier attributes with an attractive look. In combination with other materials, they particularly suitable for snack packaging, covers for thermoformable containers such as yogurt cups or refill bags for cosmetic products.

Ground coffee and kibbles remain dry in these packaging and retain their full flavour for a long time.

For tomatoes, better use Pet-met film instead of aluminium foil!

In the particular case of acidic, alkaline or salt-containing foods, metallized PET films are a perfect substitute for aluminium foils, as a longer exposure or a large contact area of aluminium with those materials, for example like: tomatoes, lemon juice, eggs, among others, can forward the potentially harmful emission of aluminium into the edible content.

Insulation systems, for example for insulation against heat radiation in buildings or for the production of vacuum insulation panels, can also be realized with metallized PET films. In addition, PET met films can be used for decorative adhesive tapes. Labels made from metallized PET-film are highly resistant to heat and chemicals, which ensures a long-time durability.