This invention relates to a composite shield assembly 10 for use in deposition apparatus 11 defining a work piece location 16, the assembly including: a first shield element 13 for position circumjacent the work piece location and a second shield element 14 for extending around and carrying the first element wherein the thermal conductivity of the first element 13 is greater than that of the second element 14 and the elements 13, 14 are arranged for intimate thermal contact.