Atomic layer deposition (ALD) techniques were used to fabricate W/Al2O3 superlattices with high X-ray reflectivity on flexible Kapton((R)) polyimide and polyethylene naphthalate (PEN) polymer substrates. Reflectivilies of 78% and 74% at lambda = 1.54 A were measured for 6-bilayer W/Al2O3 superlattices on Kaptong((R)) polyimide and PEN, respectively. These excellent X-ray reflectivities are attributed to precise bilayer thicknesses and ultrasmooth interfaces obtained by ALD and smoothing of the initial polymer surface by an Al2O3 ALD layer. The conformal ALD film growth also produces correlated roughness that enhances the reflectivity. These W/Al2O3 superlattices on flexible polymers should be useful for ultralight and adjustable radius of curvature X-ray mirrors. (c) 2007 Published by Elsevier B.V.