A new method was developed to measure how twisty paths are in materials made of fibers. By studying how easily air flows through these materials, scientists found that the twistiness decreases as the material becomes more holey. The twistiness also goes down when the fibers get thicker, but goes up when the material itself gets thicker. This new approach considers not only how many holes are in the material, but also the size of the fibers and how thick the material is.