The importance of dynamic uniaxial extensional viscosities (DUEVs) relative to shear viscosity and viscoelastic parameters in the onset of ribbing, web growth, and fiber formation in roll application is illustrated with water‐soluble polymer blends. The blends consist of variable component ratios of high‐molecular‐weight, water‐soluble polymers of different segmental rigidities. The blends provide non‐Newtonian aqueous solutions varying in dynamic uniaxial extensional viscosities, but with identical shear viscosities at a given shear rate over a104 s−1range. As the DUEV of these “same‐shear viscosity,” non‐Newtonian fluids is increased an earlier onset of ribbing is observed. After onset, a decrease in the number of ribs is observed with increasing DUEV of the fluid; the decrease is associated with growth in web size. Increasing the radius of the roll effects an earlier onset of ribbing, but the number of ribs formed at higher peripheral velocities and smaller nip spacings decreases relative to smaller radii rolls.