The use of cellulose nanofibers (CNF) as a coating layer or in pigmented coatings is promising owing to the potential for these fibers to increase the stiffness of the product. The rheological properties of typical coating slurries for paperboard with different levels of CNF are investigated as well as pure CNF suspensions. Double coated samples are prepared by rodcoating and characterized in terms of stiffness. CNF increases the viscosity of the coatings, causes a yield stress, and generates noticeable viscoelasticity in the coatings. Coatings that contain CNF increase the stiffness of paperboard around 20% compared to coatings that do not contain CNF. Carboxymethyl cellulose (CMC) at 4 wt% of the solids acts as a rheology modifier for the CNF suspensions and makes it possible to coat moderate solids levels of CNF onto paper. CMC-containing coating layer of CNF increases stiffness of substrates by 14% for 7 g/m2 coat weight. In addition to the experimental findings, using a finite element model for the bladecoating process, blade forces are predicted and are found to scale linearly with the high shear rate viscosity of the coating slurries.