In the real world, many materials may contain or develop small cracks and defects that arise from the manufacturing process or through aging. Since many applications often require the designed material to undergo a multitude of high impact loading cycles, it is crucial that such cracks do not propagate to prevent catastrophic failure. As a consequence, the determination of fracture toughness has become increasingly important for the characterization of tough hydrogels. Unlike the toughness W (material's resistance to fracture), fracture toughness specifically measures a material's resistance to crack propagation. By measuring fracture toughness, the performance of a material in the presence of small cracks can be evaluated and whether it can withstand loadbearing conditions. Fracture toughness is measured in various modes, most commonly with a pure shear test or a trouser tearing test (Figure ).