This thesis processes the work and the analysis of the design of a new adjustable harness for firefighters. It also contains marketing ideas that goes together with the new product. The concept has been developed for Interspiro AB on Lidingö in Stockholm and will be used as a help in continues development of the product for the future. The thesis contains studies regarding ergonomics, anatomy and anthropometry, material science, laws and regulations as well as interviews and other information from the company and the users. These studies have been carried out based on a version of the systematic problem solving method to suite the companies needs. The thesis is not just illustrating the development of an adjustable harness it also deals with the modification of colours, buttons and contrasts all to create a new universal feeling for Interspiro products to reinforce their trademark and enhance usability.