Which of the following materials is most likely to require a higher heat for adjustments?

Metals typically require higher heat for adjustments compared to the other materials listed. When working with metal frames, especially those made from materials like stainless steel or titanium, a significant amount of heat is necessary to make any adjustments or alterations. This is due to metals having a higher melting point and requiring more energy to change shape effectively.

Additionally, metals cannot be reshaped as easily at lower temperatures, which is often sufficient for materials like cellulose acetate, cellulose propionate, or Optyl. Those plastic materials can typically be adjusted at much lower temperatures, allowing for quick and effective changes without the risk of damaging the frame. In contrast, if a metal frame is not heated adequately, the risk of breaking or working ineffectively increases, highlighting the need for higher temperatures when making adjustments to metal eyewear.