This study aimed to identify the microstructural parameters of the crust which can explain the crispness of French fries. The French fry microstructure was visualized by X-ray micro-computed tomography (XMT). Analysis of the images provided information on the pore size distribution, global porosity of the French fries and local porosity of the crust region. The results revealed that prefrozen French fries do not practically undergo any volume shrinkage during frying. The total porosity created in French fries corresponds to the volume of water loss during frying. The difference between hot-air fried and deep-fat fried French fries was mainly related to the pore diameter and pore size distribution in the crust. Principal component analysis between the sensory and morphometric parameters showed that the volume of small pores (diameter < 0.15 mm) and the span of the pore size distribution in the first millimetres of the crust correlated with the crispness of the product (r > 0.85, P value < 0.05). Thus, a French fry is crispier if the pores generated in the crust have a small median diameter (diameter < 0.2 mm), as well as a large dispersion of pore diameters.