Biophilic design seeks to connect people with nature in the built environment. Growing research supports such nature‐based inclusion in the built environment, yet little detailed guidance exists for how to integrate it. This study used systematic development, testing, and expansion of the Biophilic Design Matrix (BDM) for the incorporation of biophilia specifically for interior design. McGee and Marshall‐Baker developed the original BDM based on Kellert's proposal of biophilic attributes, and it was initially applied in a healthcare setting. To make it more valid and reliable, this study further developed the BDM through cognitive testing with interior design practitioners in another setting type. This included the participants assessing the BDM and completing pre‐ and postquestionnaires. It also guided the finalized BDM development that now contains six elements and 54 attributes. The findings demonstrate that the interior design practitioners' use of the BDM increased perceived knowledge of biophilic design. The modified version is now called the Biophilic Interior Design Matrix (BID‐M), which is valid for biophilic interior design identification. The BID‐M also offers assistance with biophilic inclusion throughout the design process and, as such, can support the more integral incorporation of nature‐based features in the design of interior environments. The finalized biophilic interior design vocabulary should be useful to help designers include thoughtful biophilic variety for unique application, thus assisting with a “do‐it‐yourself” approach.