The SB latex moves with the water as it evaporates from the surface or gets trapped in the paper fibers during the drying of the coating. This leads to binder migration of the latex to the surface of the coating and into the paper leaving a latex-depleted layer in the interior of the coating. Clearly, the Raman spectra show that the level of depletion in the inte- rior is higher for anionic coatings than the cationic coatings and this is the reason for the lower strength for the 7 pph all-anionic coating versus the 7 all-cationic coating. Clearly, it is not a difference in the mobility between the cationic and anionic SB latex as the same level of SB latex accumulates at the surface of their respective coatings. The difference occurs at the paper/coating interface. The cationic SB latex arriving at the paper interface encounters negatively charged cellulose fibers. The charge-charge interactions fix the SB latex to the paper fibers, and this impedes additional SB latex from migra- tion into the base paper. However, this is not the case for the anionic SB binder which leads to more SB latex penetrating to the base paper through pores in the paper and leading to a larger deficit of latex in the middle of the coating layer, lead- ing to a weak binder layer within the coating layer (see Fig. 6).