What materials are classified as fire-retardant?

Fire-retardant materials are specifically designed to resist ignition and slow down the spread of fire. This means that such materials undergo treatment processes that enhance their ability to withstand flames and high temperatures, thereby providing extra time for people to evacuate and reducing potential damage to structures.

In contrast, waterproof materials are designed primarily to repel water, which does not necessarily equate to fire resistance. While some materials made of metal can exhibit fire-resistant properties, not all metals inherently provide fire retardancy, as their behavior in fire situations can vary widely. Materials with high thermal conductivity may allow heat to pass through easily and can actually contribute to fast fire spread, as they may heat up quickly and facilitate flames moving from one area to another. Therefore, the classification of fire-retardant materials aligns with their primary purpose of enhancing fire resistance and controlling flames, which is captured by the correct answer.