What material is NOT acceptable for constructing a bumper as per the inspection requirements?

In the context of the inspection requirements for bumpers, plastic is not considered an acceptable material for construction. This is primarily due to the safety and durability standards that must be met for vehicle components. Bumpers are designed to absorb impact and protect the vehicle and its occupants during a collision. While plastic can be lightweight and inexpensive, it may not provide the necessary structural integrity and resistance to impact that a bumper must have.

Other materials, such as metal, wood, and durable composite materials, can offer better protection and resilience, making them suitable for bumper construction. Metal, for instance, is known for its strength and ability to withstand impacts. Wood, although not common in modern automotive design, can be treated and reinforced for specific applications. Durable composite materials combine the advantages of light weight with enhanced strength characteristics, making them suitable for use in various automotive components.

Thus, plastic's inherent limitations in meeting crash safety standards and the overall requirement for durability in bumper construction clarify why it is considered unacceptable for this application.