Fun Home is drawn in black line art with a gray-green ink wash. Sean Wilsey wrote that Fun Home's panels "combine the detail and technical proficiency of R. Crumb with a seriousness, emotional complexity and innovation completely its own." Writing in the Gay & Lesbian Review Worldwide, Diane Ellen Hamer contrasted "Bechdel's habit of drawing her characters very simply and yet distinctly" with "the attention to detail that she devotes to the background, those TV shows and posters on the wall, not to mention the intricacies of the funeral home as a recurring backdrop." Bechdel told an interviewer for The Comics Journal that the richness of each panel of Fun Home was very deliberate:
It's very important for me that people be able to read the images in the same kind of gradually unfolding way as they're reading the text. I don't like pictures that don't have information in them. I want pictures that you have to read, that you have to decode, that take time, that you can get lost in. Otherwise what's the point?
Bechdel wrote and illustrated Fun Home over a seven-year period. Her meticulous artistic process made the task of illustration slow. She began each page by creating a framework in Adobe Illustrator, on which she placed the text and drew rough figures. She used extensive photo reference and, for many panels, posed for each human figure herself, using a digital camera to record her poses. Bechdel also used photo reference for background elements. For example, to illustrate a panel depicting fireworks seen from a Greenwich Village rooftop on July 4, 1976, she used Google Images to find a photograph of the New York skyline taken from that particular building in that period. She also painstakingly copied by hand many family photographs, letters, local maps and excerpts from her own childhood journal, incorporating these images into her narrative. After using the reference material to draw a tight framework for the page, Bechdel copied the line art illustration onto plate finish Bristol board for the final inked page, which she then scanned into her computer. The gray-green ink wash for each page was drawn on a separate page of watercolor paper, and combined with the inked image using Photoshop. Bechdel chose the greenish wash color for its flexibility, and because it had "a bleak, elegiac quality" which suited the subject matter. Bechdel attributes this detailed creative process to her "barely controlled obsessive-compulsive disorder".