Ultrafine surface-treated fillers for thin breathable films

A breathable film with a basis weight from 1 to 10 g/m2, the breathable film comprising at least one thermoplastic polymer and a surface-treated filler material, wherein the surface-treated filler material comprises

• A) at least one calcium carbonate-comprising filler material having
• a weight median particle size d50 in the range from 0.1 μm to 7 μm,
• a top cut particle size d98 of ≤15 μm,
• a fineness (<0.5 μm) such that at least 15 wt.-% of all particles have a particle size of <0.5 μm, and
• a residual total moisture content of ≤1 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material, and
• B) a treatment layer on the surface of the at least one calcium carbonate-comprising filler material comprising at least one mono-substituted succinic anhydride and/or at least one mono-substituted succinic acid and/or salty reaction product(s) thereof in an amount of from 0.1 to 3 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material,
• wherein the at least one thermoplastic polymer is selected from the group consisting of high density polyethylene (HDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), ultra-low density polyethylene (ULDPE), very low density polyethylene (VLDPE), and mixtures thereof.