Electrical Wire: THHN vs THWN vs Romex vs XHHW

Close up of blue building wire with colorful blurred wires in the background

In the world of building wire, there are several common choices available that at first appear quite similar. Here we examine some of the most common of them; THHN, THWN, Romex and XHHW. This guide will help explain the differences and make your choice of wire more straightforward. 

What is THHN Wire?

Thermoplastic High Heat-resistant Nylon-coated wire (THHN) is a single conductor wire with PVC insulation and a nylon jacket. It’s commonly used in conduit as electrical wire for buildings. Its heat and oil resistance makes THHN a suitable wire for appliances and machine tools.

What is THWN Wire?

THWN is essentially the same as THHN and the two are often used interchangeably. THWN is also a single conductor wire with PVC insulation and a nylon jacket. 


The key difference is the “W” in the name indicates water-resistance. THWN is rated for temperatures up to 90°C in wet conditions vs 75°C for THHN.




T = Thermoplastic

T = Thermoplastic

T = Thermoplastic

HH = High Heat Resistance

H = Heat Resistance

W = Water Resistance

H = Heat Resistance

W = Water Resistance

N = Nylon Coating

N = Nylon Coating

N = Nylon Coating

Temperature Rating = 90°C (Dry)

Temperature Rating = 90°C (Dry), 75°C (Wet)

Temperature Rating = 90°C (Dry & Wet)

What is Romex Wire? 

When we think of Romex, we most commonly are referring to the trade name for Thermoplastic-Sheathed Cable (TPS). Romex is often used as residential wiring for electrical circuits and lighting. We generally think of a specific type of Romex, which is known for its nonmetallic sheathing and primary use as branch wiring. This is referred to as Romex NM-B.

THHN vs Romex Wire

Romex is essentially multiple THHN wires together in a single PVC sheathing. There are some very critical differences when it comes to code compliance. Romex (or other brands of NM-B cable) is not permitted in commercial applications or residences taller than three stories. Romex may also present some challenges for installation with conduit as larger conduit may be required compared to the same gauge of THHN. Some communities do not allow the use of Romex, so be sure to check with local codes before using.

What is XHHW Wire?

Cross-Linked Polyethylene High Heat-resistant Water-resistant Wire (mercifully shorthanded as XHHW) is a single conductor electrical wire used primarily for commercial and industrial building applications. 


'The “X” in XHHW (generally abbreviated as XPLE) is an insulation material that is more resistant to wet environments than THHN (90°C vs 75°C). It’s also a thicker insulation that can better protect against breakdown when exposed to extreme environments.