According to NEC standards, what characteristic does the letter N in Type THWN insulation indicate?

The letter N in Type THWN insulation designates that the wire has a nylon covering. This nylon layer provides additional protection against moisture, chemicals, and abrasion, enhancing the durability and performance of the wire in various applications. The presence of nylon contributes to the wire's overall resilience and makes it suitable for use in wet or potentially hazardous environments as per National Electrical Code (NEC) standards. The distinction of Type THWN is particularly important for ensuring that electrical installations are safe and reliable under specific conditions.