THHN vs. XHHW-2: What's the Difference?

Written November 2018 | Lee Perry, Engineering Manager at Service Wire Company

Thermoplastic and thermoset are two common types of cable insulation, and it's important to understand their strengths and weaknesses when designing and building a new facility, machine, or appliance.

Factors That Set XHHW-2 Apart from THHN

THHN/THWN-2 is a thermoplastic product. It uses a thinner PVC insulation, which can lead to current leakage and dielectric breakdown in demanding circuits or from chemical or environmental exposure. It emits toxic smoke when burned and is less flexible at cold temperatures.

XHHW-2 is a thermoset product. Crosslink products like XHHW-2 have XLPE insulation instead of PVC, which is more resistant to chemicals, ozone, and abrasions. Because of the chemistries involved, modern XLPE is far less toxic than PVC in the event of fire. XHHW-2 is also more flexible than THHN and is more advantageous for projects where complex, close-spaced bends are required.

Wire Type

Thermoplastic (PVC)


Thermoset (XLPE)

Insulation Type Thermoplastic Thermoset              ◀BEST
Voltage Rating 600V 600V/1kV               ◀BEST
Dielectric Constant
(Hospital Grade must be 3.5 or less)
5.0-6.8 3.1                               ◀BEST
Minimum Temperature -10° C -40° C                        ◀BEST
Maximum Short Circuit Temp. 150° C 250° C                       ◀BEST
Resistance to Leakage Current
(in water MegOhms in 1,000 ft.)
Low Extremely High    ◀BEST

Acronyms Explained

T = Thermoplastic X = Cross-Linked Polyethylene (XLPE)
HH = High Heat Resistant HH = High Heat Resistant
W = Water Resistant W = Water Resistant
N = Nylon Jacket (Not Required)
-2 = Temperature Rated 90°C Wet/Dry

-2 = Temperature Rated 90°C Wet/Dry


THHN/THWN-2 is a thermoplastic product, while XHHW-2 features thermoset insulation.


  • Cheaper than Thermoset
  • Nylon Coating - Required for the Insulation System's Rating
  • Uses Thinner PVC Insulation
  • Lower Overall Electrical Insulating Properties


  • Hospital Grade
    (low leakage insulation)
  • Dual Rated 600V/1kV
  • Uses XLPE (cross-linked) Insulation Instead of PVC
  • Substantially Higher (better) Insulation Resistance


ServicePro-X No Pulling Lubricant Required Logo


Service Wire is now stocking a new line of cross-linked products, including:

ServicePro-X® eliminates the need for pulling lubricant, requires less pulling force, and is Hospital Grade. 


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