The invention discloses deagglomerated barium sulphate which has an average primary particle size of less than 0.5 μm and is coated with a dispersant. The dispersant has preferably reactive groups which are able to interact with the surface of the barium sulphate; particularly preferred dispersants are those which are able to endow the barium sulphate with a hydrophilic surface and have reactive groups for coupling to or into polymers. Also disclosed is a plastics premix comprising the deagglomerated, coated barium sulphate.