Calcium Carbonate (Calpet) Loading Rate: How Much to Add & How Much It Saves

In short: "Loading" is what percentage of calpet (filler masterbatch) you blend into resin — not the CaCO₃ percentage. Typical ranges: woven sacks 5–30%, film 5–20%, injection higher (verify per product). Raw-material saving per kilogram ≈ loading × (1 − calpet price ÷ resin price) — as an illustration, a 20–30% loading saves roughly 8–15% per kilogram. But there is one important catch: because CaCO₃ is about 3× denser than plastic, for products sold per area or per length (film, pipe), the per-unit saving is far smaller than the per-kilogram figure — unless you down-gauge.

How much calpet you can add is set by the application and the properties the product must keep. The more critical the mechanical properties, the lower the safe loading.

• PP woven sacks / raffia: 5–30%. Keep around 15% or less for fine denier so tape tensile strength holds; coarse high-denier tape tolerates more, and some is pushed to ~40% — but only with a coated fine grade and a matching draw ratio. (In raffia tape, calpet at sensible loadings actually helps — it reduces the tendency of the tape to split when oriented.)
• PE blown film: 5–20%. At thin gauge there is less room for filler because the film must stay strong and tear-free; some film is pushed to ~25% with the right grade and process.
• Injection molding (thick / non-critical parts): above the film range, and can go higher still. Thick parts tolerate more filler without losing function — but the number is very product-dependent, so verify with a line trial, not an assumption.
• Pressure pipe: low. Mechanical properties (pressure rating, long-term crack resistance) are critical, so there is little room for filler.

All the figures above are masterbatch-into-resin percentages — which brings us to the most common misunderstanding below.

This is the number-one source of confusion when buying filler. There are two different numbers, and swapping them produces wrong cost decisions:

1. CaCO₃ content inside the calpet — how much CaCO₃ is INSIDE the calpet pellet. Typically 70–85% by weight (the rest is PP/PE carrier resin plus about 2–3% additives such as wax and stearic acid). See our filler masterbatch / calpet guide for detail.
2. Calpet loading into resin — how much calpet you blend into virgin resin at your machine.

Because calpet is only ~80% CaCO₃, part of your "loading" is actually still resin (the carrier). For example:

A masterbatch loading of 25% × CaCO₃ content of ~80% = only ~20% actual CaCO₃ in the finished product. The other 5% is carrier resin.

The consequence is real: when a supplier or colleague says "25% filler," ask whether they mean 25% calpet or 25% CaCO₃ — the two differ by about a quarter in mineral content. Concretely: a quote pitched as "25% CaCO₃" delivers more mineral than one pitched as "25% calpet" (~25% vs ~20% actual CaCO₃), and because the saving formula below uses the calpet figure, comparing two quotes on different bases silently overstates one supplier's saving by roughly a fifth. Every loading and cost figure in this article is stated as a calpet (masterbatch) percentage unless noted otherwise.

High loadings (approaching 40%) demand a matching resin MFI and draw ratio, plus a fine coated grade. Raise gradually and trial on the line before committing.

Calpet saves money because it costs less per kilogram than virgin resin: you replace some expensive resin with cheaper pellets. The logic is simple:

Raw-material saving per kilogram ≈ loading × (1 − calpet price ÷ resin price).

The numbers below are illustrative — not actual prices. Take virgin resin = index 100, and calpet in the 55–65 range (for illustration, assume calpet costs roughly half to two-thirds of resin per kilogram — use your own prices). With calpet ≈ 60:

How to read it: at 20% loading with calpet priced at 60% of resin, raw-material cost drops about 0.20 × (1 − 0.60) = 8% per kilogram. If the price gap is wider (calpet only half of resin), the same saving rises to ~10%.

Two things decide whether this saving is real:

• The price gap. The saving depends entirely on how much cheaper calpet is than resin. If resin prices fall and the gap narrows, the saving shrinks with it — sometimes below the point where it is worth the quality risk.
• Quality holding. The saving only materializes if tensile strength, dispersion, and surface quality stay within acceptable limits. Over-loading to save money can raise costs instead — through product rejects, customer complaints, and line downtime.

And there is one more, subtler catch — the one that makes the per-kilogram numbers above misleading for many products.

The savings above are per weight. But many plastic products are not sold or used by the kilogram — film is sold per area, pipe and profile per length, many goods per piece of fixed size. This is where density changes the arithmetic.

One scope note up front: this catch applies to products specified by thickness or dimensions — film by gauge, pipe, fixed-size molded parts. Products specified by weight or denier — including most PP woven sacks and raffia, the largest filler application in Indonesia — keep the full per-kg saving, because the spec itself is mass-based.

CaCO₃ is far denser than plastic:

Because CaCO₃ is about 3× denser, adding filler raises the compound's density. As a result, one kilogram of filled compound makes a smaller volume (and a smaller area at the same thickness) than one kilogram of pure resin. Put the other way: to make the same area/length/volume, you need more mass of filled compound. (At 20% calpet ≈ 16% actual CaCO₃ by mass, the compound runs ~1.02 vs 0.92 g/cm³ — about 11% denser.)

An illustrative example on PE film at 20% calpet loading:

What happens: the ~8% per-kg saving is cancelled by needing ~11% more mass to cover the same film area — at this loading the per-area saving is essentially gone (and at a tight price gap, slightly negative). A wider calpet-to-resin price gap pulls it back toward break-even, but never restores the full 8% per-kg figure.

So why do film converters still use filler? Because they down-gauge: CaCO₃ adds stiffness, so a thinner film stays stiff enough for its job — where stiffness, not tear or impact, is the limiting property. Cutting thickness ~10–20% restores the per-area economics — that is where the real saving comes from, not from replacing resin in a film of the same thickness. There is also a second saving the per-resin math above misses: on white or opaque products, high-whiteness CaCO₃ lets you cut back some TiO₂ — the most expensive ingredient in many formulas — for a saving on top of resin cost. (It cannot replace TiO₂ entirely; TiO₂ provides opacity that CaCO₃ does not.)

The practical rule: ask first — is your product specified by weight/denier or by thickness/dimensions? If by weight (most woven sacks, raffia), the per-kg saving applies in full. If by thickness or fixed dimensions (film, pipe, molded parts), recompute through density and plan to down-gauge to actually capture the saving.

Raising loading is not free. As the CaCO₃ fraction rises:

• Stiffness (modulus) rises, but impact strength and elongation fall. At too-high loading — or with poor dispersion / too-coarse particles — the product turns brittle: stress-concentration points and crack initiation sites appear. (Whether filler makes plastic brittle is a question of its own — it depends on loading, fineness, dispersion, and coating; it is not automatically "yes.")
• Dispersion risk rises. At high loading, it matters more that every particle wets out and spreads without clumping. Uncoated fine grades are precisely the ones that clump — so high loadings generally demand a coated grade. When to choose coated vs uncoated is covered in our coated vs uncoated guide.
• Processing and moisture get less forgiving. High loading requires a matching resin MFI and draw ratio; on sacks, keep fine denier at ~15% or less. It also raises sensitivity to moisture and to dispersion defects — dry and store the filler properly, and expect line issues (die plate-out, bubble instability on film, screen-pack pressure on tape) to surface sooner. A coated grade helps with both.

There is no universal "maximum loading" — the limit emerges from the interaction of application, grade, dispersion, and coating. The safest approach: raise loading gradually and run one lot on your line (tensile, dispersion, surface, defects) before committing to large volume.

How much calpet can you add to resin?

It depends on the application. PP woven sacks / raffia typically run 5–30% (keep around 15% or less for fine denier so tensile strength holds; some coarse tape is pushed higher, up to ~40%). PE blown film typically runs 5–20% (some film is pushed to ~25%). Injection molding for thick, non-critical parts usually runs above the film range and can go higher still — it is very product-dependent, so verify with a line trial. Pressure pipe stays low because mechanical properties are critical. These are masterbatch (calpet) percentages into resin, not CaCO₃ percentages.

What is the difference between "loading" and "CaCO₃ content"?

Two numbers people routinely confuse. CaCO₃ content is how much CaCO₃ is inside the calpet pellet — typically 70–85% by weight, the rest being carrier resin plus additives. Loading is how much calpet you blend into virgin resin at your machine. Because calpet is only ~80% CaCO₃, a 25% masterbatch loading means only ~20% actual CaCO₃ in the finished product. Always state which basis you mean when talking to a supplier.

How much does adding calpet actually save?

The logic: raw-material saving per kilogram ≈ loading × (1 − calpet price ÷ resin price). As an illustration (not actual prices), if resin = index 100 and calpet ≈ 60, then a 20% loading saves about 8% and a 30% loading about 12% per kilogram. If the price gap is wider (calpet ≈ half of resin), the same loadings save ~10% and ~15%. Savings shrink as the price gap narrows — and only materialize if quality (tensile strength, dispersion, surface) stays within acceptable limits.

Why is the per-kilogram saving not the same as the per-sheet or per-meter saving?

Because CaCO₃ is far denser than plastic — about 2.7 g/cm³ versus PP ~0.905 and PE ~0.92. Adding filler raises the compound's density, so one kilogram of filled compound makes a smaller volume (and a smaller area at the same thickness). For products sold or counted per kilogram, the per-kg saving applies in full. But for products sold per area (film), per length (pipe/profile), or per piece of fixed size, you need more mass to make the same product — so the per-unit saving is smaller than the per-kg figure, and can even disappear, unless you down-gauge using the added stiffness.

What is the maximum loading before the product has problems?

There is no single number — the limit is set by the application, grade fineness, dispersion quality, and coating. As loading rises, stiffness rises but impact strength and elongation fall, so the product can turn brittle; the risk of film tears and clumps also rises if dispersion is inadequate. As a guide: keep fine-denier woven tape at ~15% or less; thin film typically 5–20%; high loadings demand a fine coated grade and a matching resin MFI. The safest approach: raise loading gradually and run a line trial before committing volume.

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Need help setting the right loading and grade for your product? Tell us — product type, application, the resin you run, and your cost target — and our team will respond with a matching grade, the right documentation, and advice on running a one-lot line trial.

We supply premium GCC (ground calcium carbonate) — as powder and as calpet (filler masterbatch), coated and uncoated, high-whiteness (approaching 98%) — sourced directly from Vietnam and ready to ship to Indonesia, alongside the China-origin resin you already import, handled as one relationship. Tell us the application, whiteness, and mesh you need.

See also: Filler Masterbatch (Calpet) & Calcium Carbonate for Plastics in Indonesia: A Buyer's Guide.