The material group that is not typically used in Aeronautical Engineering is ceramics, because they are too brittle.
While ceramics have some desirable properties, such as high-temperature resistance and low density, their brittleness limits their application in aeronautical structures where materials must endure varying stress conditions, impacts, and fatigue without fracturing. Aeronautical components often require ductility and toughness, which ceramics generally lack.
The other material groups listed, such as composites and polymers, are used in aeronautical engineering but come with specific considerations. Composites are often favored for their strength-to-weight ratio and versatility, despite cost concerns. Polymers can also be used in certain applications, although their usage is typically in areas where lower structural strength is acceptable. The assertion that aeronautical materials must be isotropic is not entirely accurate, as anisotropic materials like composites are widely utilized for their strength characteristics in specific orientations.