the present invention concerns double - walled microcapsules with an outer thermoplastic wall and an application process thereof on substrates , namely textile substrate . the microcapsules are applied to fibres so as to produce a slow release of products such as fragrances , antimicrobial , insecticides , antioxidants , vitamins or they can be used as materials such as thermochromic pigments , that change colour when heated , or “ phase change materials ” , that convey thermal insulation / control .