Material File System ?

I’m starting to learn Unreal and am curious about an important issue. How does Unreal store the material’s resources in the file system? If I’m using multiple texture files (normal maps and such) for one object, does Unreal call all of those files from storage during the run of the game or is it all stored in one material file? This is important when planning out a highly optimized game. Thanks for any answers.

Textures are generally stored as DXT or BC5 textures