Which property best describes an isotropic material?

An isotropic material is best characterized by having consistent properties in all directions. This means that regardless of the orientation in which the material is measured, its mechanical and thermal properties remain the same. For instance, the Young's modulus, thermal conductivity, and strength of an isotropic material do not vary with directional changes. This uniformity is crucial in many engineering applications where predictable material behavior is essential.

In contrast, materials that exhibit variable properties based on direction are classified as anisotropic, and they can behave differently depending on the direction of load or force applied. The other options, such as having only elastic properties or not changing shape, do not adequately capture the essence of isotropy in materials. Isotropic materials can be elastic, plastic, or exhibit different deformation characteristics, but it is their directional uniformity in properties that truly defines them.