A method of preventing or minimising the formation of haze in a biaxially oriented polyester film during the annealing of said film above its glass transition temperature, said method comprising: (a) selecting a biaxially oriented polyester film having glass transition temperature (Tg (° C.)); (b) disposing a coating on one or both surfaces of said biaxially oriented film; (c) annealing said coated biaxially oriented polyester film at a temperature above its glass transition temperature, wherein said coating composition is selected from: (i) an organic coating comprising a low molecular weight reactive diluent; an unsaturated oligomer; a solvent; and a photoinitiator; (ii) an organic/inorganic hybrid coating comprising a low molecular weight reactive component and/or an unsaturated oligomeric component; a solvent; and inorganic particles, and optionally further comprising a photoinitiator; (iii) a predominantly inorganic hardcoat comprising inorganic particles contained in a polymerisable predominantly inorganic matrix; and (iv) a composition comprising a cross-linkable organic polymer selected from polyethylene imine (PEI), polyester and polyinylalcohol (PVOH), and a cross-linking agent.