Absorbent capacity in a highly porous air-laid and needle punched nonwoven web was measured and a model was developed to characterize the capacity. From the model, web thickness was evaluated as a key parameter in determining the capacity. The test cell in GATS(gravimetric absorbency testing system) was modified to measure web thickness during the absorption process. The independent variables considered in the experiment were the fiber type, the fluid type, the web structure, and the environmental pressure. All the variables significantly affected the web thickness and thus absorbent capacity. The results could be clearly rationalized based on the developed model.