Which of the following materials is not commonly used for insulation?

Rayon fibers are not commonly used for insulation because they do not possess the thermal resistance and insulative properties typically required for effective insulation. Insulation materials are generally sought for their ability to resist heat transfer and maintain energy efficiency within buildings.

In contrast, materials like fiberglass, cellulose, and polystyrene are widely recognized for their excellent insulating capabilities. Fiberglass is known for its high R-value, which measures thermal resistance, making it a popular choice in residential and commercial buildings. Cellulose, made from recycled paper products, provides good insulation and is often treated for fire resistance, making it both eco-friendly and efficient. Polystyrene, available in rigid foam boards or beads, also offers superior insulation properties, serving well in various applications including wall sheathing and roofing.

Therefore, rayon fibers do not meet the criteria for effective thermal insulation, making them an uncommon choice in insulation applications.