Throughout nature, hair-like structures can be found on animals and plants at many different scales. Beyond ornamentation, warmth and a sense of touch, hair is also a natural responsive material that interfaces between the living organism and its environment by creating functionalities like adhesion, locomotion, and sensing. Inspired by how hair achieves those properties with its unique high aspect ratio structure, we are exploring ways of digitally designing and fabricating hair structures. This work presents a computational method of 3D printing hair structures. It allows us to design and generate hair geometry at 50 micrometer resolution and assign various functionalities to the hair. The ability to fabricate customized hair structures enables us to create super fine surface texture; mechanical adhesion property; new passive actuators and touch sensors on a 3D printed artifact. We present applications to show how the method can be used for designing everyday interactive objects.