An electrical socket back box 1 comprises an inner casing 2, an outer casing 4 and an integral layer of insulating material 6, which may be acoustic mastic. The inner casing 2 and outer casing 4 are composed of a hard plastic material. The insulating material 6 provides insulation of up to 64 dB acoustic rating and 2 hours fire rating. The layer of insulating material 6 is press moulded onto the rear surface of the inner casing 2 and the outer casing 4 is press moulded onto the layer of insulating material 6.