As computational technology and new materials are entering the world of textiles, our view on the textile material is challenged; the areas of textile design and interaction design start to merge. Designing interactive textiles means communicating new expressional forms through textile material. This thesis aim to contribute to the exploration of designing interactive knitted textiles with focus on linking interactive properties, especially visual and tactile, to different ways of expressing them. Design examples and experiments presented are meant to show new possibilities for designing textile material able to change structure, colour and temperature in different ways in response to environmental stimuli. As a way of presenting, and reflecting on, these interactive properties, a notion of expression diagrams is introduced.