Abstract: An inexpensive, lightweight reflective assembly member having good optical quality is provided. The reflective assembly is particularly adaptable to accommodating temperature variations without providing destructive thermal stresses and reflective slope errors. The reflective assembly may consist of a thin lamina reflective surface member and a lightweight substrate member of cellular structure. The respective materials may be chosen so that the coefficient of thermal expansion will be approximately the same. The substrate can comprise a cellular glass block while the reflective lamina member can be a thin sheet of glass with appropriate reflective coating. The lamina and cellular substrate member can be bonded together to form the reflective assembly. The method of fabrication includes abrading the cellular substrate with an abrasive master die to form an appropriate concave surface.