The file extension P3M identifies default files for materials (textures) of the image editing software Adobe Photoshop. P3m files include the material and texture properties, such as gloss, reflection, and how to lay a 2D texture on a 3D object.
These materials can be used to add surface features and textures to 3D objects in 3D scenes. The ability to work with 3D model data is only available in the extended version introduced since version CS3. Photoshop extended offers the possibility to import different 3D formats (eg 3DS Max) or to create objects yourself.
If you create a 3D layer, you have access to the various 3D settings windows. You can load P3M files (or select the defaults) and save them in '3D (Materials)'.
P3M files are usually placed under 'Preferences / Materials' in the main Photoshop folder. By default, various specifications are already installed. (eg wood, steel, chrome)