Abstract: The paper discusses the design and technology problems of planar, large-scale sonar arrays. It covers the fundamental operating parameters that bring the original array design to the requirements of an actual sonar system and briefly discusses state of the art technology issues. The main part of the paper includes a description of array design using PU elastomers in the volumetric filling version. This material is used both for the internal framework, the casing, sealing housing and the coupling layer. The author highlights the limitations and risks of using polyurethane to manufacture planar sonar arrays, especially those for deep water operation. Examples of designs and technological problems are given and discussed. They are the result of many years of experience gathered in the designing and testing of arrays made for the various sonar systems at the Department of Acoustics and Department of Polymers of the Technical University of Gdansk.