The shear and extensional behavior of two aqueous gum solutions, namely (1) 1-20 g/L guar gum (Torres et al., Food Hydrocolloids. 2014; 40: 85-95) and (2) kappa/iota-hybrid carrageenan solutions (5-20 g/L), are shown to exhibit Giesekus-fluid behavior when in the semidilute regime. In this regime, a common set of Giesekus fluid parameters described both shear and extensional behavior. A new analytical result describing the extension of a Giesekus fluid in the filament stretching geometry is presented. This also gave reasonable predictions of the Trouton ratio. Higher concentration guar solutions, in the entangled regime, yielded different Giesekus fluid parameters for extension to those for simple shear. The extensional data for all concentrations of both gums collapsed to a common functional form, similar to that reported for cake batters (Chesterton et al., J Food Eng. 2011;105(2):332-342); the limits of the new filament thinning expression provide insight into this behavior. (C) 2014 American Institute of Chemical Engineers