The beryllium windows are used to separate the vacuum of the beamline from the vacuum of the storage ring and the air in the experimental hutch. Beryllium is a special element, which is very transparent to X-rays. To reduce absorption losses, the thin sheet of metal is only 300 µm thick. Special care has to be taken during fabrication and handling of the windows to avoid breakage. The Beryllium sheets used at the PUMA beamline have been soldered to water-cooled copper pieces, to dissipate the heat caused by the X-ray beam.