The thermal stability of carboxymethyl cellulose (CMC), kappa carrageenan (KC) and partially hydrolyzed polyacrylamide (HPAM) was evaluated in aqueous solution, by monitoring the viscosity of polymer solutions as a function of aging time at temperatures between 40 and 120 °C. The concept of half-life decomposition was used to determine the viscosity decay constant (τ, the time required for the specific viscosity of the solution to fall 1/e times the original viscosity) for each polymer, by applying the exponential decay viscosity model. The HPAM exhibited the greatest thermal stability, with τ values of 63.69 and 25.31 days at 80 and 100 °C, followed by CMC with τ values of 10.25 and 2.29 days at 80 and 100 °C, and KC with τ values of 3.89 and 1.26 days at 80 and 100 °C, respectively. The methodology used in this study made it possible to predict the time needed to reach certain levels of viscosity when the polymer solutions are exposed to different temperatures.