The time it takes to mix fluids in disposable bags is a key issue for many process developers. This study demonstrates recirculation of 1 cP and 5 cP viscous solutions in 50 L, 2-dimensional (2D) pillow bags using a tubing loop and peristaltic pump. This method is particularly applicable to cross flow filtration. The results show that good mixing in relatively short time can be achieved when sufficiently high recirculation flow rates are used. Many times well mixed solutions are attained in three minutes or less.