Switchable mirrors based on magnesium-yttrium alloy thin films were prepared by a direct-current magnetron sputtering method. The changes in the film thickness of the mirrors due to hydrogenation and dehydrogenation have been investigated using atomic force microscopy and X-ray reflectometry. As a result of first hydrogenation of a switchable mirror, the thickness was expanded by similar to 15%, while as a result of dehydrogenation, the thickness was compressed by only similar to 2%. From the switching processes, the thickness changed by similar to 2% on the following optical switching. This small change may cause high switching durability of Mg-Y switchable mirrors. (C) 2013 Elsevier B.V. All rights reserved.