The design of textiles is flexible. The soft, pliable nature of textiles means that their expressiveness and physical properties can be altered long after the material has been produced, by e.g. adding or removing colour, pattern, density, or by printing, laser-cutting, etc. This transformability means that the design of textiles can be further developed in another design process in relation to a specific product or context. In the emerging field of textiles produced using 3D modelling and additive manufacturing, structures can be defined in detail and, later, altered or completely redesigned in CAD programs. However, the designs of these textiles are generally fixed when the structures emerge from the 3D printer. This paper describes a practice-based project that explores the transformability of 3D printed textiles, considers the question of whether some of the openness that characterises their digital form can be introduced to their physical form, and then explores what form this could take. It begins by describing the project which forms the basis for the exploration, the outcome of which thus far consists of two experimental 3D printed textiles with changeable physical structures. It then discusses the considerations and decisions involved when designing for such transformable textiles, proposing ways to understand and describe what is taking place: First, by relating them to the considerations made when defining open design systems; second, by introducing two types of design decisions, which together define which aspects of the textile’s design are closed to further development, and which are open for others to develop.