Product lifetimes and obsolescence have been central points of discussion in the fashion field. In this context, design researchers and practitioners have proposed a variety of strategies to enable slower cycles of product replacement, leading to smaller volumes of clothing production and consumption. A previous review of these strategies, however, revealed that there is no empirical evidence of their efficacy in terms of lifetime extension or environmental sustainability. Therefore, this research takes a first step in covering this knowledge gap. It proposes methods to assess the impact of such approaches and applies them to the specific case of “product personalisation” the strategy most frequently mentioned in literature. Clothing has characteristics that are not present in other product categories common in lifetimes studies. These characteristics enable comparative analysis of products, diachronic studies over relatively short periods of time, and estimations of the environmental benefits of lifetime extension. Taking advantage of such particularities, the article evaluates the environmental gains of personalised products by comparing their performance with ready-made garments in terms of age, usage, influence on new product demand, and waste. The research is based on a series of wardrobe studies and company interviews. The outcomes of these studies question the environmental benefits of product personalisation. When compared with ready-made garments, personalised garments were not kept for longer time, nor were they used more frequently. Moreover, no evidence of their contribution to reductions in new product demand and waste was found. These findings confirm the need for more empirical research to understand the effect of this and other design strategies aimed at delaying clothing obsolescence and reducing production volumes and waste. Such enquiries can provide relevant feedback to practitioners developing creative solutions. In that way, empirical research and creative practice can benefit from each other's input and build iterative cycles that ensure effective actions. The methods advanced in this study aim at supporting this valuable line of research, leading to a more environmentally-sound apparel sector.