As written by FerrariMan96. Mas files are fairly easy. All you need to do is: - download ISI's MAS tool (I assume you have already done that ) - Open the MAS tool and Import all of the textures (you can make this easier by sorting the files by 'file type' and highlighting all the textures of one type, eg DDSs... import... BMPs... import etc.) - Once that's done, people generally save/export it as TEXTURES.MAS, <<YOURTRACK>>MAPS.MAS or <<YOURTRACK>>_TEXTURES.MAS - Do the same for all of the .GMT files, and again, people generally save/export it as MODELS.MAS, <<YOURTRACK>>.MAS or <<YOURTRACK>>_MODELS.MAS - As a safety measure, at this point I add all of the files to a Zip, 7Zip or RAR file and put it on my desktop, Incase I missed a file or two. - Delete all image and model files that you added to the MAS archives, leaving behind the .AIW, .CAM, .GDB, .SCN and .TDF files, of course as well as the two .MAS archives. - Open up the .scn file and find the lines which start with "MASFile=". - Enter two new lines - "MASFile=<<Your texture MAS file>>" and "MASFile=<<Your models MAS file>>", eg "MASFile=MODELS.MAS" and "MASFile=TEXTURES.MAS" Now start up rFactor and see if it works! If you have I or two models or textures missing, as rFacotr will tell you, open up the MAS tool again, open the appropriate .MAS file and add the missing files.