What is Magnet Wire?

The term “magnet wire” is used to describe solid conductor wire (usually copper), insulated with a polymer based film. The films are designed to provide a uniform dielectric coating while taking up as little space as possible.

In selecting & specifiying a magnet wire, there are several areas of concern:

  1. Size or Diameter
  2. Insulation Thermal Class
  3. Insulation Build or Thickness
  4. Additional Characteristics such as color or addition of bondable coating
  5. Or you can specify parallel bonded magnet wire in copper or any alloy.

Parallel bonded magnet wire


Although copper is the primary conductor material due to its superior conductivity & relatively low cost, other metals & alloys may be utilized.

Thermal Classes

There are a variety of film insulations available for magnet wire offering different characteristics. The primary classification factor for magnet wire is “Thermal Class.” Thermal class is the recommended maximum continuous operating temperature for the insulation. Standard thermal classes range from 105 degrees Celsius up to 240 degrees Celsius.

Insulation Builds:

Insulation “build” refers to the thickness or the amount of insulation applied. The industry standard builds are as follows:

  • HEAVY (Sometimes called “double”)

Note: SINGLE & HEAVY are the most common.

NEMA (National Electrical Mfrs Association) publishes a set of standards for magnet wire (NEMA MW 1000) which includes dimensional values for the various sizes & builds. Our *WireTronic Wire Info Software* has a dimensional data section based on the NEMA standards.

Guide to Insulation Callouts:

  • Thermal Class 105 C, NEMA MW 2-C,15-C Polyurethane (solderable @ 360 C, standard color is RED)
    Formvar (Cryogenic use, oil filled transformers, superior abrasion resistance, non-solderable)
  • Thermal Class 155 C, NEMA MW 79-C, 80-C Polyurethane/Poly-Nylon (Solderable @ 390 C, standard color is RED)
  • Thermal Class 180 C, NEMA MW 30-C, 77-C
    Polyester-imide (non-solderable)
    Solderable Polyester-imide
    (solders @ 450C)
    Note: Addition of Nylon overcoat to above qualifies to NEMA MW 76-C, 78-C
  • Thermal Class 200 C
    Polyester Amide-Imide, NEMA MW 35-C, 74-C
    *Teflon ™ film, No NEMA spec
  • Thermal Class 220 – 240 C, NEMA MW 16-C
    Polyimide film
    Other common names:
    *ML ™
    *Kapton ™ Film
    *Teflon, Pyre ML, and Kapton are all registered trademarks of DUPONT CORP.

Bondable Magnet Wire

Bondable magnet wire is the combination of conventional film insulated magnet wire with the addition of a thermoplastic adhesive coating.

The main advantage in manufacturing is the ability to construct free-standing coils (coils without bobbins). The adhesive coatings are designed to be activated by heat (such as when baking in an oven) or solvents. Sometimes a combination of heat & solvent works best depending upon the specific application.

Bond Coatings

  • Polyvinyl Butyral 105 C
    Heat Activation: 120 – 140 C
    Solvent: Alcohol (Isopropyl)
  • Epoxy 130 C
    Heat Activation: 130 – 150 C
    Solvent: Acetone or Methyl Ethyl Keytone (MEK)
  • Polyester 130 C
    Heat Activation: 130 – 150 C
    Solvent: Methyl Ethyl Keytone (MEK)
  • Modified Polyester 155 C
    Heat Activation: 220 – 260 C
    Solvent: None