The emergence of the Smart Textiles field opens possibilities for designers to combine traditional surface fabrication techniques with advanced technology in the design process. When it comes to the field of Smart Textiles as interactive materials for space design, it is essential to understand the identity of the material through design and also to understand the novel expressions being mediated for space. Thus, the purpose of this thesis is to develop knowledge by design on Smart Textiles as materials for architecture and to do so through design. The thesis formulates a research program to frame the design explorations. Thus, Relational Textiles for Space Design is defined as a research program in architecture where the focus lies on developing methods to design interactive textile surfaces using knitted constructions. The program is illustrated by the design projects e.g., Knitted Light, Touching Loops, Designing with Heat and Tactile Glow. As a result of the research, a new methodological framework for interactive textile design is proposed. The framework defines the notions of field and frame of reference for the design. These notions form a method to discuss design variables of relational textile expressions. Based on the design examples, the emerging expressions are described according to the field relations that the interactive textile introduces in space. Thus, expressions of spatialization e.g., reduction, amplification, addition and disassociation are introduced.