There is an engineering paradox that travels every day on thousands of trucks and cargo ships: a container that weighs just over 2 kg is capable of lifting and protecting over 2 tons of material. If we were to compare this proportion to the animal world, we would be close to the performance of spider silk.

But there is no magic behind this strength, but rather refined physics applied to polypropylene (PP). In this article we explore how the woven weave of a Big Bag can support up to 2,000 times its own weight.

It all starts at the molecular level. Polypropylene is a thermoplastic polymer characterized by high tensile strength. During the extrusion process, the material is stretched to align the molecular chains in a specific direction-this process dramatically increases the strength of the individual yarn (or “band”).

However, a band is fragile when taken individually. The real strength of a Big Bag comes, in fact, from its weaving. Most FIBCs use a circular frame technology, which creates a continuous tube of fabric without side seams.

In a circular weave, the warp (vertical) and weft (horizontal) threads work in synergy. When the bag is filled, the hydrostatic pressure of the inner material pushes outward. The weave distributes this force evenly over the entire surface, avoiding points of stress concentration that would lead to tearing.

Unlike steel, however, PP fabric has a slight elasticity. This allows the Big Bag to absorb dynamic shocks (such as during a sharp lift) without breaking.

Increasing the density of the yarns means increasing the number of“contact points” in the weave. The denser the weave, the smaller the sliding space between the threads, making the sack a truly flexible shell.

In SebinoPack, physics is put to the test in rupture tests. A Big Bag designed for 1,000 kg (5:1 standard) must be able to withstand a pressure of 5,000 kg before it fails. This margin of safety is guaranteed not only by the quality of the raw material, but by the precision with which the polypropylene strips are woven and sewn together.

A Big Bag is not a simple “plastic bag,” and at SebinoPack we know this well. In fact, for us, it represents the result ofcareful textile engineering, where the density of the yarn and the geometry of the weave create a structure capable of defying gravity. Choosing the correct weight means ensuring that your “web of steel” is perfectly calibrated for the value it must carry.