Fillers are the cheapest way to make paper better and cheaper at the same time. They raise opacity and smoothness and replace part of the fibre. The question most mills face is not whether to use a filler, but which one – and how much.
The three common choices
China clay (kaolin)
China clay has flat, plate-like particles. It gives excellent smoothness and printability, works in acid and neutral systems, and is the classic filler for writing and printing paper.
Calcite powder
Calcite powder is a natural calcium carbonate. It is brighter than most clays and cheaper per tonne, so it lifts brightness while lowering cost.
GCC (ground calcium carbonate)
GCC is finely ground limestone or marble with a controlled particle size. It gives high brightness and good opacity and is widely used in neutral and alkaline papermaking.
How they compare
- Brightness: GCC and calcite are usually brighter than clay.
- Smoothness and print: clay wins thanks to its plate shape.
- pH: carbonates need neutral or alkaline conditions – in acid systems they dissolve and foam. Clay works almost anywhere.
- Cost: carbonates are typically cheaper per tonne.
- Strength: all fillers reduce strength as loading goes up; use cationic starch or DSR to compensate.
Blending is often the answer
Many mills blend clay with calcite or GCC: carbonate for brightness and cost, clay for smoothness and print. The right ratio depends on your grade, wet-end pH and target ash.
Use cases
- Writing & printing: clay + GCC blends for brightness and print.
- Kraft and liners: low filler levels, often clay, for surface.
- Duplex board: filler in the top ply; coating clay on the surface.
- Ceramics and paints: the same minerals serve ceramic and paint makers.
Before you switch fillers
- Confirm your wet-end pH suits the new filler.
- Check retention – a new filler may need a different retention aid dose.
- Measure ash, brightness, opacity and strength on reels.
- Agree consistent lots and 50 Kg bag or bulk packing.
Not sure which filler fits? Tell us your grade, pH and current filler – we will suggest a blend and send samples. Ask about fillers →