These Physically Based (PBR) Materials are optimized for photo realistic rendering in game engines (e.g. Unity 3D, Unreal) and rendering software (e.g. Blender, Autodesk Maya). PBR materials are designed to work in all lighting conditions, and always look consistent, like they would in real life. That's why in the creation process, it's important to have good reference images from different angles to get reflectance and color values right. They consist of Albedo, Metal, Smoothness (inverted Roughness), Normal, Height and Occlusion Maps, seamlessly tileable in one or both directions.
Some of these materials are created shooting photos with a DSLR camera, then retouched and processed on the computer. Others (like the Tatami mat material) are created entirely in 3D because of difficulty finding well lit real world examples. This also applies for difficult camera angles like roofs, glass and metals.