While most acoustic material properties are standardized today, the way of digitally storing such data is not. Commercial applications, internal developments and open-source solutions usually use their own proprietary file formats that make a data exchange practically impossible. This circumstance led to the foundation of openMat. This cooperative project aims at defining a standard for the storage of both standardized acoustic material properties and supplemental meta-information. In the current conceptual design, openMat supports the following material properties: absorption-, scattering- and diffusion coefficients as well as bidirectional transfer functions and complex impedances. In addition, meta properties are assignable to each material, e.g., multilingual material description, information on pricing and data acquisition, and additional files such as textures and 3D models. Using such meta-information makes the database already applicable during the early and graphical design stage of a room. The project proposes an Extensible Markup Language (XML) database format since XML is human- readable, machine-processable, and a de-facto standard today. However, the openMat project provides not only the database specification, but also a huge example library, plug-ins and an open source, platform- independent database editor with convenient graphical user interface and comprehensive manual. All content is freely available on the project site www.openMat.info.