The research aims to develop a new restoration approach for leather in cultural heritage having lost its flexibility after exposure to heat. This innovative method relies on the use of biological molecules in order to respect the nature of the object and preserve its past and future. To confirm the protein aggregation expected after exposure to heat, the leather was first characterized by different techniques; then the innovative restoration approach was tested. The characterization of heat-damaged leather was performed by both physico-chemical (DMA, TGA, contact angle measurement, SEM) and biochemical (Protein extraction, Protein assays, Western-Blot) methods. Heat induces darkening, mass loss, shrinkage, stiffness increase and renders leather non wettable. Part of these changes can be due to an aggregation of leather proteins as a result of heat exposure as also shown by sequential protein extraction. Thanks to this new information, a biochemical restoration approach using enzymatic hydrolases aiming to break the protein aggregates has been developed. One of the challenges was to provide water for the enzyme without wetting the leather surface so to avoid further damage of the leather. Several procedures were tested and compared, and encouraging results were obtained.