3, 5, 7 layers or "nano": what the layer count in stretch film means

Why stretch film has layers

Stretch film is made by co-extrusion: several extruders melt different polymers, which are joined into one film as they leave the die. Each layer can then be designed for its own job, for example:

• skin layers for cling on one side and slip on the other;
• core layers for strength, stretch and puncture resistance.

See cast vs blown stretch film for how the film itself is made.

From 3 layers to dozens

A 2015 article in Plastics Technology magazine, written by experts from a resin maker, a die maker and a winder maker, traced how layer counts grew:

What "nano" means

There is no formal standard. The same article describes the industry's developing consensus: a "nanolayer film" is one in which most layers are thinner than one micron. In a cast film, a layer can be as thin as about 100 nanometres, and stretching the film by more than 300% makes it thinner still. By that definition even some 9- and 11-layer films count as nanolayer films, and all 20–50 layer films do.

Why more layers can help

The article explains the benefit with a "plywood effect": thin layers of different polymers have different crystal structures and reinforce each other, which improves properties such as puncture and tear resistance and allows thinner layers of high-performance polyethylene. In one example from the resin maker, a 15 µm nanolayer film delivered similar physical properties and almost the same holding force as a 17 µm reference film, with considerably less film weight.

Independent tests point the same way: in a 2021 laboratory study (Tkaczyk et al., Sensors), a pallet wrapped with a multilayer film at 300% stretch passed a 0.5 g test with about half the film of a standard 23 µm film, which failed.

Is more always better?

Not by itself. The same article stresses that the gains come from combining the right polymers with the layer structure, and that more layers demand much tighter precision in the feedblock and die. A film with more layers made from ordinary materials is not automatically better than a well-designed 5- or 7-layer film. When you compare films, ask for performance data (stretch, puncture and tear resistance, holding force), not only the layer count.

What it means for rewinding

A rewinding machine does not change the layer structure: it comes with the jumbo roll. Thin, high-performance films need well-controlled tension; rewinders with independent servo control of unwinding and rewinding, such as the SM-1300 2S and SM-1300 2S PRO, let the operator set the tension from the touchscreen for each jumbo roll. See how to choose jumbo rolls.