Passenger-to-freighter conversion is a common practice in the aviation industry, especially for older civil aircraft that have completed their passenger service missions. Converting these aircraft into freighters extends their operational lifespan by several years, significantly increasing the overall economic benefits throughout their life-cycle. The main cargo compartment lining is a crucial component of the P2F conversion process, It must meet the requirements outlined in CCAR-25. This paper, based on experiences in civil aircraft Passenger-to-freighter conversions, examines the CCAR-25 regulations, verification methods, and qualification criteria applicable to main cargo compartment lining systems, with a focus on important aspects of these regulations.