The paper presents a linear theory of elastic materials with voids, which differs from classical linear elasticity by treating the volume fraction of voids as an independent kinematical variable. The authors, Stephen C. Cowin and Jace W. Nunziato, derive the basic equations and formulate boundary-value problems, establishing uniqueness and weak stability for the mixed problem. They apply the theory to several applications, including homogeneous deformations, pure bending of a beam, and small-amplitude acoustic waves, determining the change in void volume induced by these deformations. The paper also discusses the relationship between the proposed theory and the effective moduli approach for porous materials, suggesting that both theories complement each other in understanding the mechanical behavior of materials with voids. The linear theory is described in detail, including the balance equations and the treatment of volumetric rate effects, which are crucial for understanding the stress-strain response and the propagation of acoustic waves in such materials.The paper presents a linear theory of elastic materials with voids, which differs from classical linear elasticity by treating the volume fraction of voids as an independent kinematical variable. The authors, Stephen C. Cowin and Jace W. Nunziato, derive the basic equations and formulate boundary-value problems, establishing uniqueness and weak stability for the mixed problem. They apply the theory to several applications, including homogeneous deformations, pure bending of a beam, and small-amplitude acoustic waves, determining the change in void volume induced by these deformations. The paper also discusses the relationship between the proposed theory and the effective moduli approach for porous materials, suggesting that both theories complement each other in understanding the mechanical behavior of materials with voids. The linear theory is described in detail, including the balance equations and the treatment of volumetric rate effects, which are crucial for understanding the stress-strain response and the propagation of acoustic waves in such materials.