RC may be inappropriate for substances which strongly adhere to metal surfaces or that are non-compactible. The robustness of RC can also be affected by the variability in drug substance physical and mechanical properties; however, less so than in direct compression. In general, depending on the compression and flow properties of the drug substance, the drug load can vary from 2 to 50% in RC. Kleinebudde has listed possible problem areas with regard to processing using RC. The main issues are: i) high amount of fines/leakage of uncompacted material, ii) loss in compactibility, iii) homogeneity of the ribbon and, iv) extensive sticking of material to the rolls.