A composition comprising a plastics material, an inorganic particulate solid such as aluminium trihydrate and a coupling modified of formula A-(X—Y—CO)m(O—B—CO)nOH wherein A is a moiety containing a terminating ethylenic group with one or two adjacent carbonyl groups; X is a direct bond, O or N; Y is C1-18-alkylene or C2-18-alkenylene; B is C2-6-alkylene; m is from 1 to 4 and n is from 0 to 5 provided that when A contains two carbonyl groups adjacent to the ethylenic group then X is N. Specific examples of coupling modifiers are β-carboxyl ethylacrylate and 5-carboxy pentyl maleimide.