The Porcelain Enamel Institute (PEI) rating system categorizes tiles based on their durability and wear resistance. It ranges from PEI 0 to PEI 5, with higher numbers indicating greater durability. PEI 0 tiles are unsuitable for foot traffic, while PEI 1 tiles are suitable for low-traffic areas. PEI 2 tiles are appropriate for residential use, PEI 3 for commercial use, PEI 4 for heavy-duty commercial use, and PEI 5 for heavy-duty industrial use. The PEI rating is crucial in selecting tiles for specific applications, ensuring optimal performance and longevity.