Runnability and coating property effects of five viscosity builders - carboxymethylcellulose (CMC), hydroxyethyl cellulose (HEC), sodium alginate, soy protein, and an alkali-reactive, acrylic-vinyl acetate latex - were examined in styrene-butadiene (SBR) latex-air knife coating formula applied to a folding boxboard on a pilot machine. The high-molecular weight viscosity builders (CMC, HEC, and sodium alginate) were used at 0.4per thousand (on pigment) and soy protein and the reactive latex were used at 7per thousand, replacing a portion of the SBR binder. Investigative techniques included: (1) construction of a theoretical model of the coating process, including approximation of shear rates, (2) rheological measurements by an impact method, the Weissenberg Rheogoniometer, and the Hercules HiShear viscometer, (3) stop-action photography of coating blow-off, and (4) use of black paper mist-collection strips on the lower lip of the air knife. Observations of a basic nature included: (1) differences in coating visoelasticity and misting, (2) differences in coverage of a wire mark in the base stock, (3) differences in extent and uniformity of K&N ink absorbency, and (4) instances of a coating wave pattern, the proposed caused of which is vibration in the air jet.