Published: November 3, 2026 | Last Updated: November 3, 2026
SEO Title Tag: PP vs Sepiolite Fibre: Which One for Your System | Hezhen Meta Description: Polypropylene and sepiolite fibre are often quoted against each other but answer different questions. Service temperature, dosage, water behaviour and the substitutions to avoid.
Polypropylene fibre and sepiolite fibre appear on the same enquiry lists, are sold into the same construction channels, and are frequently quoted against each other on price per kilogram. They are not alternatives. One is a synthetic polymer whose job is to hold a crack closed; the other is a natural mineral whose job is to hold a wet system in suspension. Choosing between them on price per kilogram is how projects end up with the wrong additive at the right cost. This guide sets out the two thresholds that decide most cases, what each fibre actually does inside a mix, and the substitutions that should never be made.
Threshold One: Service Temperature
The clearest dividing line is heat, and it is not close.
Polypropylene softens at roughly 140–150 °C, melts at roughly 165–173 °C, and begins to oxidise and embrittle well below that — ageing accelerates above about 130 °C. Sepiolite keeps its structure to around 350 °C in continuous service and only melts near 1650 °C. Anything that involves fire resistance, kiln or furnace proximity, hot-service sealing, or a process temperature above the polypropylene range belongs to sepiolite, and no amount of dosage adjustment will change that.
There is a subtler point in the other direction. Sepiolite carries zeolitic water that leaves the structure at around 110 °C. That does not destroy the mineral, but it does change how it behaves in a water-based system: over-dried sepiolite loses much of the rheology and water retention it was bought for. If a supplier offers a high-temperature-calcined grade for a wet mortar application, ask why. Drying is for moisture control, not for performance.
Threshold Two: Dosage, and Why Price per Kilogram Misleads
The two products are dosed at completely different orders of magnitude, which makes unit price a poor comparison.
Polypropylene fibre in concrete is typically added at 0.6–1.2 kg/m³. In a cubic metre of concrete weighing roughly 2,300–2,400 kg, that is about 0.03–0.05% by mass — a few hundred grams doing a structural job. Sepiolite in a coating, putty or mortar is typically dosed at a fraction of a percent up to a few percent of formulation weight; at 1% of a mix weighing around 2,000 kg/m³, that is about 20 kg per cubic metre.
So sepiolite is used at roughly twenty times the mass of polypropylene for the same cubic metre. Comparing them on price per kilogram therefore compares two numbers that never meet in the same formula. Compare cost per cubic metre, or per square metre of finished surface, and compare it against what the additive replaces — a rheology modifier from another chemistry, or a steel fibre dosage in the tens of kilograms. That comparison usually reverses the conclusion.
Four Systems, Four Answers
| System | Primary job | Choice | Reason |
|---|---|---|---|
| Concrete slab, pavement, screed | Shrinkage crack control, impact and impermeability | Polypropylene | Forms a three-dimensional network that bridges micro-cracks |
| Putty, tile adhesive, skim coat | Anti-sag, anti-settling, open time | Sepiolite | Thixotropic network restores structure when movement stops |
| Fire-resistant board, intumescent coating, hot-service seal | Keep the system intact at temperature | Sepiolite | Inorganic; no fuel load; does not melt |
| Low-cost dry-mix filler, partial substitution | Cost reduction in general putty | Either, partly | Both thicken, but behaviour differs and must be re-tested |
What Each Fibre Actually Does
Polypropylene works mechanically. Its fibres are fine — typically 10–50 μm in diameter, with a tensile strength around 460 MPa or better — and they disperse through a mix as individual filaments. Before the concrete hardens, that network interrupts the capillaries that feed plastic shrinkage cracks; after it hardens, the same filaments bridge micro-cracks and absorb impact energy. It does not thicken a mix, does not hold water, and does not change rheology. It is also completely hydrophobic, with a moisture regain close to zero, which is why it performs in wet and marine conditions without absorbing anything.
Sepiolite works structurally and rheologically. Its needles interlock rather than disperse as separate filaments, and the internal channels give it a large surface that holds water. That is why it thickens, prevents sag, keeps heavy filler suspended, and extends open time. It reinforces by interlocking rather than by bridging, so it improves toughness and green strength but is not a substitute for a crack-bridging fibre at concrete dosage. It is also strongly hydrophilic — the mirror image of polypropylene.
Two products, opposite water behaviour. One repels water to survive in it; the other holds water to make a wet system work.
The UV Question, Answered Properly
Polypropylene is chemically inert but not photo-stable on its own. Unstabilised fibre exposed to sustained sunlight embrittles and loses strength, which is why outdoor and geotextile applications require a UV-stabilised grade. A data sheet that says "resistant to UV" without specifying the grade is describing the stabilised version and implying it applies to all.
Two qualifications keep the claim honest. First, stabilisation extends service life; it does not make the fibre immortal, and the exposure matters more than the years. Second, UV stability and thermal stability are different properties, and a UV-stabilised fibre still softens at the same temperature as any other polypropylene. Both limits should appear on the same line of the specification.
Sepiolite does not have this problem — it is an inorganic oxide and does not degrade in sunlight — but it has a different one: it holds water, so moisture pickup in packing and storage is the failure mode to manage.
Reading It Regionally: Southeast Asia and the Gulf
In Southeast Asia, humidity and heat push the choice in two directions at once. For concrete work the fibre of choice is polypropylene, and the specification point is a stabilised grade plus a length that suits the application — 6, 12 or 19 mm for concrete, not the 38–102 mm textile staple sold for nonwovens and carpets. For coatings and putty applied to damp walls under strong sun, sepiolite earns its place through sag control and water retention. The friction aftermarket — scooter and motorcycle brake linings, a continuous consumable in this region — is sepiolite territory, and it is where the asbestos substitution actually happened.
In the Gulf, the fire codes and the ambient heat do the deciding. Anything in a fire-rated assembly, a hot-service seal or an exterior coating under relentless sun belongs to sepiolite. Concrete anti-cracking still belongs to polypropylene, with the caveat that a dark surface in Gulf summer is not the place to rely on an unstabilised grade.
Five Substitutions to Avoid
- Polypropylene into a fire-rated or hot-service system. It melts and adds fuel. No dosage compensates.
- Sepiolite as a drop-in for concrete crack control. It thickens and toughens, but it does not bridge a shrinkage crack at the dosage a fibre is expected to deliver.
- Attapulgite for sepiolite. They are close relatives with similar rheology but different composition and morphology; treat it as a formulation change and re-test.
- Textile staple for concrete fibre. Long denier-count staple will ball in a mixer; concrete wants short cut lengths.
- Unstabilised polypropylene outdoors. It will fail on exposure, not on load.
What to Ask Before Ordering
For polypropylene: grade and stabilisation, cut length, diameter, tensile strength, moisture regain, and whether the lot certificate covers dispersion. For sepiolite: fibre length class, whiteness, moisture at packing, whether the surface is modified, and the packing specification for a sea voyage. In both cases ask for lot-to-lot consistency data rather than a single headline figure, because the buyer's formulation was tuned to one behaviour.
Frequently Asked Questions
1. Can I use sepiolite instead of polypropylene in concrete? Not as a crack-control fibre. Sepiolite improves rheology, water retention and green strength, but it does not form the bridging network that limits plastic shrinkage cracking at normal fibre dosage.
2. Can I use polypropylene in a fire-resistant board? No. It softens in the 140–150 °C range and melts around 165–173 °C, and it adds fuel load. Fire-rated and hot-service systems require an inorganic fibre.
3. Which one works in salt water or marine conditions? Polypropylene, because it is chemically inert and does not absorb water. Sepiolite is the better choice where a mineral additive must build viscosity in brine, as in salt-tolerant drilling and sealing work.
4. Does sepiolite lose performance if it is dried hard? Yes, in a wet system. Its zeolitic water leaves at around 110 °C, and over-dried material loses much of its rheology and water retention. Specify drying for moisture control, not as a performance step.
5. Are the two ever used together? Yes, in putty and mortar systems where both rheology and crack resistance matter. The usual approach is sepiolite for sag and water retention, with a small polypropylene addition for shrinkage cracking, and the pair validated on a trial batch.
Next Step
Send the system, the service temperature, the mixing water chemistry and the performance the additive has to deliver. The Hezhen technical team will recommend one fibre or a combination, confirm the grade, length class and stabilisation against your specification, and supply trial quantities so the dosage can be fixed on your own formulation before an order is placed.
