TREMIN 939 is the name for a surface-treated filler that is produced from natural wollastonite by iron-free grinding with subsequent air separation and coating with an organo-silicon compound. TREMIN 939 is characterized by its distinct needle-structure.

The type of surface treatment is defined by the following three-letter code added to the characteristic grain data:

AST treated with Aminosilane
MST treated with Methacrylsilane
ZST proprietary surface treatment
MSST treated with Methacrylsilane special
EST treated with Epoxysilane
RST treated with Trimethylsilane
ESST treated with Epoxysilan special
USST treated with Aminosilan special