The KiCad 3D model library supports two file formats:
WRL files contain material properties and are used for realistic rendering. However they cannot be exported to MCAD packages.
KiCad v4.x and lower can only render WRL files
STEP files are used for integration with MCAD software packages. These files do not contain material properties and cannot be used for realistic rendering.
KiCad v5.x and above can render STEP files directly in the 3D viewer
Only models provided in these file formats will be accepted.
It is suggested that a .WRL and .STEP version of the model are provided simultaneously. This provides options for both high quality rendering and MCAD integration.