There is a growing emphasis on designing with people with diverse health experiences rather than designing for them. Yet, collaborative design becomes difficult when working with individuals with health conditions (e.g., stroke, cancer, abuse, depression) that affect their ability or willingness to engage alongside researchers and verbally express themselves. The present paper analyzes how the clinical practice of art therapy engages these individuals in cocreative, visual expression of ideas, thoughts, and experiences. Drawing on interviews with 22 art therapists and over two years of field work in a clinical setting, we detail how art therapists view making as expression for people with complex communication needs. Under this view, we argue that art therapy practice can inspire collaborative design engagements by understanding materials as language, creating space for expression, and sustaining expressions in a broader context. We discuss practical and ethical implications for design work involving individuals with complex communication needs.