Good point, Joe ... For those who do not know, stand-alone THWN cables are coated in PVC, as opposed to vinyl, to assist in water resistance. THHN wire is typically two-conductor with ground, and found in the familiar ROMEX cabling that wires homes, e.g. 12-2. The coating also explains the slight price difference between the two ... and the noticeable price difference between ROMEX cabling (cheaper) and THWN stranded cabling. In harsh climates these are important differences to know!