THHN Vs. THWN: Which Is The Better Building Wire?

Jessica Stone
by Jessica Stone
Choosing the right type of wire for construction can be difficult, but THHN and THWN are among the best options. The main difference comes down to durability, and THHN is more heat-resistant whereas THWN is more water-resistant. Whether it be practical uses or resistances, let’s take a look at the difference between THHN and THWN building wires.

Electrical work is among the most complicated aspects of home improvement and construction to understand. There are so many variables between wires and conduits that affect installation and durability. So, how are THHN and THWN wires different and why does it matter?

Thermoplastic high-heat-resistant nylon-coated wires (THHN) cannot exceed 167 degrees Fahrenheit in moist settings. However, THWN wires are suitable for wet and dry conditions and are rated to withstand 194 degrees Fahrenheit. Dual-rated cables work as both THHN and THWN wires with superior heat and moisture resistance.

It used to be that you could simply use THHN wires for most applications. However, that isn’t ideal in wet conditions, particularly when THWN wires are readily available. Follow along as we explore the differences between THHN and THWN wires.

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Difference Between THHN and THWN

Both THHN and THWN are different in several unique ways, particularly when it comes to their resistance to moisture. Some wires, such as THHN wires, simply aren’t suitable to use in a moist environment. However, THHN and THWN wire have more in common than you may think, and that comes right down to their construction.

Both types of wire are coated with nylon and PVC insulation that protects them. THHN wire and THWN wire are rated for different temperatures in humid areas, but that is essentially their only difference. Now, you can buy dual-rated cables that work as both THHN and THWN wires for almost no upcharge.


Thermoplastic high-heat resistant nylon-coated, or THHN wire is among the most durable wires in construction. They can endure heat up to 194 degrees Fahrenheit and their temperature will drop to 167 in cold conditions. The wire is usually a two-conductor and you can find it in ROMEX cables on most modern construction sites.

THHN wire cannot exceed 167 degrees Fahrenheit in particularly moist areas. You get less water resistance from THHN wire than you would from THWN wire, but the durability is the same besides that. Professionals only use THHN wire in areas that are dry and will stay dry.

Some manufacturers produce an all-in-one cable that contains THHN, THWN, and THWN-2 wire. However, it is ideal to strictly use THHN wire indoors or away from wet conditions to avoid electrical damage and bodily harm. There are three main components to THHN wire:

  • Wire material: Aluminum or copper
  • Conductors: Can be solid or stranded, depending on the size
  • Jacket: Nylon outer jacket with polyvinylchloride (PVC) insulation or vinyl


Thermoplastic heat water-resistant wire, or THWN wire if preferable for moist conditions. THWN wire is made of the same conductive aluminum or copper and nylon as THHN wire, but with slight differences. The main difference is that THWN wire is rated to handle 194 degrees Fahrenheit (90 degrees Celsius) when it is wet or dry.

This means that THWN cables have more practical uses than THHN cables do. You can use THWN cables indoors or outdoors, and they work in wet and dry conditions. Some THHN wires have less water-resistant vinyl coatings, but THWN wire always has a nylon jacket.

Which is Better?

THHN wire is more effective than THWN wire, but THWN wire is better for moist conditions. Modern manufacturers produce wire that is rated as both THWN and THHN wire, and that is the best option. That way, you won’t have to worry about the moisture in the area where you lay it with dual-rated cables.

Besides their differences in moisture resistance, THHN and THWN wires are almost entirely the same. Both THHN and THWN wires are made with the same essential materials and methods. There are three main components to THHN and THWN wire:

  • Wire material: Aluminum or copper
  • Conductors: Can be solid or stranded, depending on the size
  • Jacket: Nylon outer jacket with polyvinylchloride (PVC) insulation

Perhaps the most important aspect of any THHN or THWN wire is the nylon jacket. The PVC inside of the nylon coating provides insulation and protection against physical damage or temperature changes. Dual-rated cables are generally just as well-insulated as cables that are strictly THHN or THWN.

Breaking Down the Acronyms

The names thermoplastic high-heat resistant nylon-coated wire and thermoplastic heat and water-resistant wire are too wordy. That is why we use the acronyms THHN and THWN, but that can be just as confusing because nothing obvious comes to mind. Words like heat-resistant are important when it comes to electrical work, especially with wires.

The “N” in both types of wire refers to the nylon coating that protects you and the wires. “Thermoplastic” refers to the special insulation that is resistant to heat and moisture, or both with THWN and dual-rated cables. Wire without a nylon coating may be cheaper, but it provides less protection than a THHN wire.

T = Thermoplastic
HH = High Heat Resistance
N = Nylon Coated
Temp Rating:
90° C in dry locations
T = Thermoplastic
H = Heat and
W = Water Resistance
N = Nylon Coated
Temp Rating:
90° C in dry locations and 75° C in wet locations
T = Thermoplastic
H = Heat and
W = Water Resistance
N = Nylon Coated
Temp Rating:
90° C in both wet and dry locations


You need to exercise caution whenever you do any form of electrical work, particularly when you work with wires. The thermoplastic outer jacket of THHN wire has been known to release toxic gases when burned. It is strongly urged that these wires are positioned within conduits to prevent the release of any toxic materials.

THHN wires use a thinner PVC insulation and this is a key factor when it comes to the wire’s electrical characteristics. Because the insulation is thinner, it can often cause a current leakage or even a breakdown during environmental or chemical exposures.

You should consult with the National Electrical Code or any other relevant electrical codes in your area before beginning electrical work. As always, if you ever feel unsure or uncomfortable about what you are doing, consult a licensed electrician.

Advantages of THHN Wires

If you need a building wire that is strong and effortlessly handles heat, there’s no doubting that THHN wire is the route to go. However, using this type of cable comes with several other additional advantages:

  • Handles high voltages. THHN wire can manage up to 600 volts. Its copper conductor allows it to handle such high voltages without any issues.
  • Wet and dry application. You are no longer limited to a particular climate or environment with dual-rated wires. Most THHN wires can now be used in settings that are both wet and dry.
  • Durability. The strong jacket makes it resistant to damage and abrasion.
  • Affordability. THHN is a very cost-effective choice for building wire. You can often find many deals by just simply searching the internet. It’s much more affordable than XHHW building wire.
  • Can save you energy and time. The flexible nylon coating makes THHN very easy to manipulate and install.
  • Simple application. THHN wire comes color-coded making it very easy to install.
  • Comes in a variety of different sizes. Possibly one of the greatest advantages of this type of building wire is that it comes in a wide variety of sizes. You are sure to find the perfect size to fit your project needs.

What is MWR?

Machine wire rated wire, or MWR is a type of small gauge wire commonly used in modern construction. MWR wire often shares a dual THHN/THWN rating and features either a nylon or PVC jacket. The thin ends that MWR has make it ideal for soldering.

However, the insulated version of MWR is not THHN/THWN rated. This type is used in the development of windings for motors and power supplies. You can commonly find MWR in auto work or in high-end power tools.

Does THHN Wire Have to be in Conduit?

A THHN wire must be in conduit or else you will violate electrical code and it can be quite dangerous. You won’t pass an electrical inspection if they find THHN wire that is not in conduit, and you’ll have to repair it to pass. Every single wire conductor must run through a conduit or else it is a violation of electrical code.

You can run THHN wire anywhere throughout your home as long as it is in conduit. It is okay to run THHN wire through a wall as long as you install a transition point that runs to the electrical box. Electrical codes require a conduit anytime that an electrical wire is exposed to prevent damage and corrosion.

Summing It Up

THHN wire and THWN wire are primarily only different when it comes to water resistance. The extra-thick PVC insulation and nylon coating on THWN wires make them easier to work with in moist conditions. You must always run a THHN or THWN cable through a conduit to ensure that it won’t get wet or damaged.

THWN and dual-rated cables are the best option if you live in a humid climate and have poor ventilation in your home. StandardTHHN wire is a superior wire, able to manage a variety of situations. A stand-alone THHN wire can only be used in dry or damp locations. However, Dual-rated cables are the best option in modern times because they work perfectly in dry and wet locations.

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Jessica Stone
Jessica Stone

Jessica considers herself a home improvement and design enthusiast. She grew up surrounded by constant home improvement projects and owes most of what she knows to helping her dad renovate her childhood home. Being a Los Angeles resident, Jessica spends a lot of her time looking for her next DIY project and sharing her love for home design.

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