The term “fusing fix” denotes the degree of permanence of an electrophotographic toner image that has been thermally attached to a paper substrate by a hot roll fuser. The widespread change from acid to alkaline papermaking for commercial copy papers was accompanied in many cases by a reduction in fusing fix. To study this problem, a set of 25 model papers was produced with three different types of internal size, three types of inorganic filler, and three types of surface treatment. The papers were extensively characterized for their chemical and physical properties, sample sets were printed in three different high-speed copiers, and the fusing fix of the resulting images was quantified by the crease test. Out of 47 measured parameters, the crease width had a significant correlation only with the dispersive component of the surface energies of the papers. A hypothesis was constructed to explain how changes in the paper constituents affect both the surface energy and fix of the papers.