A thermal energy storage composition having improved fire retardant properties comprising: A) particles of organic phase change material (PCM), B) particles of fire retarding magnesium hydroxide and/or aluminium hydroxide, and/or C) magnesia cement, in which the particles of (A) organic phase change material are distributed uniformly throughout particles of (B) magnesium hydroxide and/or aluminium hydroxide and/or throughout (C) magnesia cement. The composition is suitable for producing a variety of articles having thermal energy storage properties and/or temperature regulation. Suitable articles include fibres, fabrics, foams, heating and cooling devices and building materials.