We are developing a digital writing tool, Polymorphic Letters (PL), to investigate hand and pen movements as they may extend and enrich expression in written language. PL recognizes individual letters and associated spatial, temporal and pressure qualities of pen movements. The system maps these features to typography and colour variables, creating lively representations on-screen. Writers will use the tool in learning environments emphasizing the role of personal expressions. We explore style and voice as they pertain to expressions through hand, pen, and words, and describe the rationale for PL, its iterative design, and next steps based on writers' and readers' experiences.