A correction to van Wyk's model of the compressibility of fibrous materials

van Wyk put forward a compression model of fibrous materials utilizing a library of analytical approaches, including the continuum mechanics, stereological, geometrical probability, least square method, and excluded area concept. In this letter, we wish to point out a key error noted in van Wyk's work with the objective of correcting misconceptions that are held by the majority of us. Through this contribution, we question the "inverse cube" pressure-volume relationship of random fibrous materials. The pressure-volume relationship has been revisited by modifying the formulation of the mean length of a fiber element between consecutive contacts projected on the compression direction.