The core job of sealing film, put simply, is to block two things for your product: oxygen and moisture. Poor oxygen barrier leads to oil oxidation and vitamin loss; poor moisture barrier causes powder caking and tablet dampness. So how do you improve barrier performance? Leadtra Packaging breaks it down from three levels: materials, processes, and structure.

The most direct approach: change the material

Aluminum foil is currently one of the best common materials for barrier performance. The thicker the aluminum foil layer, the stronger the oxygen and moisture barrier, and the lower the pinhole risk. But aluminum foil isn't the only option. Metallized film (VMPET) offers good barrier properties at a lower cost, suitable for medium-shelf-life products. If transparent packaging is desired, EVOH composite film is an option — its oxygen barrier performance stands out among transparent materials, but its moisture barrier is average and typically needs to be paired with a moisture-proof layer like PE.

Structural design is also critical

A single-layer film has limited barrier capability, so multi-layer composite structures are the mainstream solution. The common approach: PET provides strength and a printing surface, aluminum foil handles the core barrier, and PE or CPP serves as the heat-seal layer. By adjusting the thickness and sequence of each layer, you can "customize" the barrier level for different products. For example, products requiring high-temperature retort would use thicker aluminum foil and heat-resistant adhesive layers; products needing moisture protection but with lower oxygen barrier requirements could use a PET/PE structure instead of aluminum foil composite.

Process control affects final performance

With the same materials, different lamination processes can produce significantly different barrier results. Adhesive coating must be uniform — insufficient coating creates micro-channels. Lamination temperature and time must be precise — too low results in weak bonding, too high causes adhesive aging that actually reduces barrier properties. Slitting and rewinding must control pinhole generation; the aluminum foil substrate itself should have a pinhole density of ≤1 per square meter.

Testing is the final verification

After improvements, data is the proof. Oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) are the two core testing indicators, measured according to methods such as GB/T 19789 and GB/T 17146. Different products have different barrier level requirements — only testing will tell you if it's sufficient.

If you're unsure whether your current sealing film's barrier performance meets your product requirements, Leadtra Packaging can help evaluate film material options, provide barrier testing recommendations, and help you find the best match.