Non-crimp stitched fabrics are becoming increasingly popular as reinforcing materials in high-performance composites due to their high mechanical properties. Hence, it is of interest to investigate the processability of this type of fabrics. Focus is here set on the permeability of the fabrics. The methods of this investigation are: (i) a theoretical analysis; (ii) microscopic studies of the geometry of the fabrics and (iii) measurements of the permeability. From the experiments, it is found that only small variations of the geometry change the permeability up to three times. Furthermore, the simple model proposed works surprisingly well in certain cases, while in others it fails to predict the permeability. From the experimental results and a comparison between the model and the experiments, some guidelines are presented how to design a high-permeable fabric.