Barriers and methods of obstructing apertures. One embodiment provides a temporary barrier that includes a bag, a fluid source, and a shear thickening fluid. The bag is made of fabric and can expand (e.g. inflate) via the fluid source which is in communication with the bag. The shear thickening fluid permeates the fabric of the bag and has two states. In the first state the shear thickening fluid allows the fabric to be flexible. In the second state the shear thickening fluid causes the fabric to be inflexible. To cause the shear thickening fluid to transition to the second state a shear must be present in the shear thickening fluid. A material that is capable of reacting to form a gas may be in communication with the fluid source to provide a gas to expand the bag. A deflation valve may also be included in the barrier.