Co-Constructed or Constrained? How AI Collaboration Tools Reshape UI Design Practice in a Time-Boxed Design Challenge

In what ways do generative AI (GenAI) tools embedded in mainstream design software affect UI design practices and outcomes? In this study, we examine the use of FigmaAI, a GenAI feature within the industry-standard platform Figma. We conducted a within-subject study with 16 professional UX designers, each of whom completed two high-fidelity UI design tasks in a think-aloud session: one conventionally, without AI, and one with FigmaAI. We analyse the design process itself alongside experiences and reflections on using and not using AI, gathered from adjacent semi-structured interviews and post-task questionnaires. Our findings suggest that GenAI reshapes UI workflows, shifting them from additive to subtractive processes: designers refine AI drafts rather than building interfaces from scratch. While AI reduces workload and accelerates initial setup, it also constrains exploration, limits perceived ownership, and produces designs that are more visually and structurally similar.