Which type of impact foam is typically less durable in lower-quality helmets?

Single-density foam is typically less durable in lower-quality helmets because it is made of one type of foam with a uniform density throughout. This characteristic limits its ability to effectively absorb and distribute the force of an impact, making it less effective in protecting the wearer during accidents or falls. Higher-quality helmets often utilize multi-density foam, which includes varying densities that can better manage impacts by allowing different layers to compress and absorb energy more efficiently. Single-density foam lacks this capability, leading to diminished performance and safety features in lower-quality helmets.