$detail

The $detail VMT parameter specifies the VTF texture to use for adding detail to the material surface.

• Greyscale image usually used (in conjunction with "$detailscale") to add higher resolution detail to the $basetexture.

Basic VMT Syntax

"$detail" "Path/DetailmapA" 
"$detailscale" float 

• where Path is the filepath relative to the game_directory/materials folder.
• where DetailmapA is the filename; ie DetailmapA.vtf.
• where float is the scale factor
• Notice the .vtf file extension is not used in VMT texture references.