Insulation class B

Isolierstoffklasse B insulation class

Insulation class B

Class B insulating material 

Class B insulating material consists of materials or combinations of materials such as polyester, mica, fiberglass, etc. with suitable bonding, impregnating, or coating materials (note, some older applications used asbestos). Other materials or combinations of materials, not necessarily inorganic, may be included in this class if it can be demonstrated by experience or testing that they can be operated at the Class B temperature.

Maximum Allowable Temperature: (IEC60034-1 & NEMA MG1-12.43): 130C, 266F.

Class B insulation materials

We focus on 4 materials in the field of insulation material class B:

  1. Mylar A brand polyester film as well as Hostaphan WN.
  2. Pressboard-polyester film-pressboard-laminate
  3. grained PSP-PET-PSP laminate
  4. Polyester nonwovens (Freudenberg Viledon H1010, Viledon H1015, Viledon H1030)

Mylar A and Hostaphan WN polyester films

Mylar A is a transparent, flexible, strong, tough and resistant polyester film based on polyethylene terephthalate (PET). Mylar A is milky opaque in thicknesses from 75 µ. Excellent resistance to moisture and most chemicals. Since it does not contain plasticizers, the polyester film will not become brittle with aging under normal conditions. Mylar 500A also offers exceptionally high strength values with its thickness of 0.500 mm. Due to its mechanical strength, Mylar A 500 is particularly advantageous for use as wedges for motor insulation, stampings and semi-rigid or rigid printed circuits.

Hostaphan WN is a white polyethylene terephthalate (PET) film particularly suitable for electrical insulation of machinery and equipment such as electric motors and generators. The film is characterized by high dielectric strength and high contact resistance.

All polyester film is suitable for use as slot insulation, deck insulation and phase insulation in motor and generator construction, as well as for use as core, layer and deck insulation in transformers, chokes and relays.

Pressboard-Polyester Film-Pressboard-Laminate

This electrical insulation material of insulation class B is a 3-layer laminate consisting of polyester film with a layer of pressboard on both sides. This laminate proves to be extremely tear-resistant and is characterized by high dielectric strength.
The layer of pressboard excellently absorbs the impregnating agents used in engine construction, thus preventing unfavorable air entrapment. This results in improved heat dissipation from the winding copper to the iron pack.

These laminates are suitable as slot insulation and slot covers in electric motors, and as layer and core insulation in transformer construction.

grained PSP-PET-PSP laminate

2-layer or 3-layer material (depending on type) with inner layer of polyester film and outer layers of grained (burled) green or brown pressboard. These properties provide good flexibility and stretchability, while maintaining a certain minimum strength. The minimum strength is necessary to be able to slide the phase insulation between the windings. Pliability prevents damage from mechanical stress during winding head deformation. This product is also available as a self-adhesive die-cut.

Polyester nonwovens (Freudenberg Viledon H1010, Viledon H1015, Viledon H1030, Viledon H 1062)

This product is a thermally bonded polyester nonwoven with high impregnating and impregnating properties and good mechanical properties. The combination of low moisture absorption, good compatibility with resins and coatings, chemical purity, low dielectric losses, high continuous temperature resistance and long service life makes it an ideal candidate for use as phase insulation.


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