A lot of CR2 files have legacy materials and if you delete all material entrys - they stay gone. But, when you open at CR2 file in Poser, it will rewrite the materials that are assigned in the OBJ file (an entry for every discrete Usemtl_*** line in the "f" section. The only way to permanently get rid of a material is to delete it from the OBJ file. If you are playing with textures in Poser and have accumulated a long list , just save the CR2 and close Poser. When reopened, the CR2 will only list the textures that are actually used, the others are gone.