Many areas of robotics, particularly locomotion and grasping, can benefit from the ability to modulate friction on surfaces that come into contact with objects in the environment. Previous research has tried to address the challenge of tunable friction; however, those efforts only provide modest gains or are difficult to integrate. We propose a tunable friction mechanism that relies on pneumatic actuation and is easily integrated into pre-existing soft actuators. We characterize the performance of our friction mechanism with quantitative force data for varying preload forces, substrate materials, and inflation pressures. Testing results show that our tunable friction mechanism achieves an order of magnitude differentiation in friction forces between high and low friction states. We demonstrate its potential application in a one degree-of-freedom soft crawler and a soft gripper with actuatable finger friction pads. The crawler successfully propelled itself forward by leveraging asymmetric strokes and the gripper achieved a factor of five differentiation of grip force between engaged and disengaged states of the friction tuning mechanism.