Politicians and planners in Europe and America in the 1930s and 1940s were increasingly anxious about the availability of wool for military requirements and actively encouraged research into substitute fibres. Innovation energised by the needs of war informed the development of processes to transform proteins normally used for food (milk, soya, corn, and fish) or perceived as waste (egg whites, chicken feathers and slaughter-house products) into fibres. This paper explores both innovative technology and conceptual models of innovation as applied to substitute fibres which were intended to result in both technical and cultural shifts. Substitute innovation was used to modify existing technology used to produce regenerated cellulosic fibres was modified to make regenerated protein fibres. Moderately successful in the unusual economic conditions of war and marketed as modernistic, patriotic and utopian fibres, regenerated protein fibres lost their price advantage to competing petrochemical fibres. Their physical disadvantages outweighed their benefits and they rapidly faded from popular memory and are only scantily represented in museum collections. The brief trajectory of these fibres prompted a revision of the traditional conceptualisation of innovation as developed by Usher and Schumpeter. Innovation is influenced by producers’ technological and tacit knowledge and skills and public policies. A new model of substitute innovation is proposed here to aid understanding of attitudes to the acceptability of new fibres which is relevant for the development, marketing and popular acceptance of today’s regenerated protein fibres. This paper will be illustrated with case studies of American and English fibres including Aralac, made from milk, Henry Ford’s soyabean fibre, Ardil made from peanuts and today’s milk and soyabean fibres, promoted as innovative, environmentally sensitive and health-giving