What type of foam is molded to the internal shape of some vehicle cavities for added strength?

The correct answer identifies structural foam, which is specifically designed to enhance the strength and integrity of vehicle components. This foam is molded to fit the internal shapes of cavities within the structure of a vehicle, effectively reinforcing areas that may be susceptible to stress and impact during operation or in the event of a collision.

Structural foam adds rigidity and support without adding excessive weight, which is a critical factor in automotive design. By being tailored to the contours of specific vehicle parts, this type of foam can effectively distribute loads and absorb energy, contributing not only to the vehicle's durability but also to passenger safety.

The other types of foam, such as collapsible foam, are generally used for cushioning or energy absorption but do not provide the same level of structural reinforcement. Loose foam is often utilized for insulation or soundproofing rather than strengthening vehicle components, and insulating foam is primarily focused on thermal resistance. Thus, the specific properties of structural foam make it the ideal choice for the application described in the question.