Paint losses are usually present in our paintings the complex behavior of canvas supported paintings makes the treatment of these damaged areas imply aesthetic and structural issues that might be considered. This paper focuses on the study of filling materials used throughout history for the completion of missing areas of the paint layer in canvas paintings. Since literature on fillers only refers to their handling properties, traditional fillers (made of hide glues), synthetic formulations and ready mixed commercially manufactured fillers were tested. Valuable information about their mechanical and dimensional properties was obtained which helped to determine which fillers better adapt to the structural behavior of canvas paintings as well as the RH allowable rank in which specific fillers can withstand moderate dimensional changes without apparent damage.