Super sacks are made almost entirely of polypropylene (PP). The body is fabric woven from flat PP tape yarns, the lifting loops are PP webbing, the seams are sewn with high-tenacity synthetic thread, and many bags hold a polyethylene (PE) liner. Coatings, UV stabilizers and conductive yarns are added as the product requires, and each choice changes what the bag can lift, hold in and keep out.
We have made industrial packaging since 1930 and produce these materials ourselves, from PP granules onward, in four vertically integrated plants. Fabric weight, coating, loop strength and stitching are engineered to the safe working load of the super sacks we build.
Every Material in One Super Sack
A standard super sack, or FIBC (flexible intermediate bulk container), typically carries 500 to 2,000 kg (about 1,100 to 4,400 lb) of dry, flowable product.
| Component | Material | What it governs |
|---|
| Body fabric | PP tape yarn woven on circular or flat looms | Safe working load, puncture resistance, tare weight |
| Coating | Thin PP film laminated to one or both faces | Dust tightness and moisture pickup |
| UV stabilizer | Additive blended into the resin | Strength retention in sunlight |
| Lifting loops | Narrow woven PP webbing | Lifting strength at each loop |
| Sewing thread | High-tenacity PP or polyester thread | Seam strength and sifting at seams |
| Liner | PE film, plus EVOH, PA or aluminum barrier layers | Moisture, oxygen, odor and contamination |
| Static control | Conductive or static dissipative yarns | Static charge |
Why Is Polypropylene the Standard Material?
Strength for its weight is the reason. PP has a density of about 0.9 g/cm³, lighter than water, and when it is extruded into thin tape and stretched, its molecular chains align and tensile strength rises sharply. An empty bag weighing a few kilograms can carry hundreds of times its own weight. PP also absorbs almost no water, does not rot like jute and resists many acids, alkalis and salts.
Its weak points explain the additives: unprotected PP breaks down in sunlight, loses impact toughness in severe cold and softens at high temperatures. The first step of our vertically integrated production process is PP extrusion, where raw materials are dosed and extruded into yarn of the required thickness and denier (the weight in grams of 9,000 meters of yarn).
Fabric Weight and Strength
Standard bag bodies commonly use fabric between 140 and 220 g/m² (roughly 4.1 to 6.5 oz/yd²), set by the safe working load, safety factor and product. A bag rated at 1,000 kg (2,205 lb) with a 5:1 safety factor must survive a top-lift test at 5,000 kg (about 11,000 lb). ISO 21898, the international standard for FIBCs carrying non-dangerous goods, applies 5:1 to single-trip bags and 6:1 to reusable ones. Sharp or angular products need heavier fabric, because puncture becomes the main threat.
Weight alone does not prove strength. Tape denier, weave density and how well the tape was stretched all change the result, and some formulations contain mineral filler such as calcium carbonate, which adds weight without adding strength. In our lab, yarn and fabric must meet set criteria in tensile and elongation tests before they are accepted for bag assembly. Some stretch absorbs lifting shock, while too much lets the bag deform.
Our PP woven fabric comes from 30 circular looms that produce tubular fabric for bodies without side seams, 20 flat weaving machines for wide fabric and 5 narrow weaving machines for narrow fabrics such as reinforcement tapes, in widths and weights set by customer specification.
Should the Fabric Be Coated or Uncoated?
Uncoated fabric is an open weave that lets air and moisture vapor pass. It suits products that need to breathe and coarse granules that cannot slip between the tapes, while fine powders work through the weave under vibration.
Coated fabric carries a thin PP film on one or both faces. We apply single or double-sided lamination depending on the product, making the surface resistant to air and water and stopping fine particles from leaking through the weave, and we confirm the result with lamination performance and sifting tests. Coating does slow the escape of air that fine powders carry in during filling, so highly aerated products may need extra settling time.
UV Stabilizers for Outdoor Storage
Ultraviolet light breaks the polymer chains in PP, so an exposed bag gradually loses strength and turns chalky on its sunny side. UV stabilizers, commonly hindered amine light stabilizers (HALS), are blended into the resin before extrusion, so the protection runs through every tape instead of sitting on the surface.
Stabilization is rated in hours of accelerated exposure rather than calendar months, because a summer in Arizona and a winter in Maine deliver very different UV doses. We verify it with an accelerated UV test. Stabilizers slow degradation without stopping it, so covered storage still matters.
Sewing Thread and Lifting Loop Webbing
Loops are made from narrow woven PP webbing, denser than the body fabric and sized to the safe working load, while many one and two loop bags form their loops from the tubular body fabric itself. Thread is high-tenacity PP or polyester. For fine powders, a filler cord or tape sewn into the seam reduces dust escaping through needle holes.
Under the IEC 61340-4-4 classification, Type C bags carry conductive threads and must be grounded during filling and discharge, while Type D fabric dissipates charge without grounding. In our FIBC test laboratory finished bags go through drop, topple, stacking and tear tests, plus conductivity and grounding tests where static control is specified.
Liner Films and Barrier Layers
A liner is a separate film bag inside the FIBC that closes the gaps in woven fabric and keeps moisture, oxygen, odor and contamination away from the product. Liners are usually polyethylene, because PE film stays flexible, heat seals easily and forms a continuous barrier. We extrude our own PE film and test liners in our lab before assembly.
- LDPE and LLDPE: flexible and easy to seal, with LLDPE adding puncture resistance.
- MDPE and HDPE: stiffer, with lower moisture vapor transmission than LDPE.
- EVOH: a strong oxygen barrier, sandwiched between PE layers because moisture weakens it.
- PA (polyamide): toughness and an added oxygen barrier.
- Aluminum: a very high barrier to moisture, oxygen and light.
- Conductive and antistatic films: for bags where static must be controlled.
US buyers often see liner gauge in mils (one mil equals 25.4 microns). Our FIBC liners can also be built for high tear strength, hot filling, aroma control and vacuum use.
Raw Materials for Food and Pharmaceutical Grades
Food and pharmaceutical bags use the same material families, but the resin grade and the production environment change. Buyers normally specify virgin food-contact resin, since recycled feedstock is hard to trace. In the US, food-contact rules for polyolefins come from the FDA, so buyers ask for documentation covering resin, liner film and printing ink.
Our food grade bags use food-contact PP fabric and are made in clean rooms, with production organized according to HACCP requirements and certified to ISO 9001 and BRCGS. Bags for pharmaceutical products such as active ingredients and baby formula are produced under clean room conditions with procedures that meet HACCP and BRCGS requirements. Coatings and multi-layer co-extruded barrier liners form the contamination barrier. We cut fabric with hot, ultrasonic and cold methods, and heat-based cuts fuse tape ends, so fewer loose fibers reach flour or milk powder.
Questions Buyers Ask About FIBC Materials
Is super sack fabric waterproof?
No. Coated fabric resists water on its surface, but seams and needle holes stay open. For hygroscopic products, the moisture barrier comes from a PE liner, often a barrier liner, plus covered storage.
Can super sack materials be recycled?
Yes. Body, loops and often thread are all polypropylene (resin identification code 5), so a clean bag without its PE liner is a single-polymer feedstock. Our PCR products are made with 30% recycled rPP granules.
Which material details belong in a quote request?
List the product, its bulk density and whether it is fine, sharp, hygroscopic or flammable, plus the safe working load, safety factor, outdoor storage time and what the liner must keep out. From those answers we set fabric weight, coating, UV level, loops and liner film, so contact our team with your product data.