AbstractWhen used as a thickening agent in aqueous suspension, hydrolyzed starch–polyacrylonitrile graft copolymer (H‐SPAN) has broadly variable rheological properties, such as viscosity, storage modulus, and stress overshoot characteristics. A series of H‐SPAN preparations with variable swelling ratioQwere made by pretreating portions of stock material. As 1% suspensions in water, they had viscosities η that were non‐Newtonian. At a constant shear rate, η of the suspensions depended onQand had a sharp maximum in the midrange ofQ. In terms of reduced concentrationcQ, wherecis weight fraction of polymer, the highest η occurred whencQwas approximately 2. With isoionic dilution, each suspension had a constant reduced viscosity function, η/cQ, providedcQ>2. The value of η/cQfell rapidly whencQapproached 1. All thickeners of the closely packed gel–particle type so far examined have this relation of the reduced variables. The shear modulus calculated from measurements of primary normal force and corrected for solvent swelling, according to theory for rubber for elasticity, was essentially constant for each suspension measured during isoionic dilution tocQ= 2. The density of crosslinks calculated from the modulus was extremely low for all samples. The variable rheological properties of the preparations resulted primarily from differences in their low effective cross