This course draws the physical association between 3D printing and materials. It defines the nature of different kinds of materials as well as the attributes which makes them 3D printable. The role of phase transformation especially temperature driven transformation in 3D printed materials is treated at the fundamental level. This course presents a lot of research based instances of material behaviour under 3D printing conditions. Practice based data are also presented to reinforce the importance of materials know-how at the industrial level.