Kraft Insulation

Transformer Layer Insulation

Transformer Layer Insulation

The work horse of electrical insulation. High dielectric strength and purity, Kraft Insulation conforms to ASTM D1305 Type 4, as well as individual customer electrical specifications. Used in transformers and capacitors.

Kraft Insulation is produced in multi-layer form on a modified wet machine from an electrical grade, unbleached Kraft wood pulp. The dry finished sheets contain no sizing, coloring or other materials which would contaminate natural or synthetic impregnating oils.

Kraft Insulation is used as transformer layer insulation, capacitor can liner and in numerous other applications where the ultimate in electrical and physical strengths are required.

Kraft Insulation is available in sheets, strips, mill rolls and slit rolls in thicknesses from .007” to .062”. Above .062” to .250” is available only in sheets and strips. Above .040” thickness Kraft is laminated from dry sheets with a polyvinyl-acetate-polyvinyl alcohol formulation having good electrical properties.


 Fiber Content 100% Unbleached Kraft Wood Pulp
 Ash Content (Max.) .75%
 pH Water Extract 6.0 – 7.5
 Moisture Content 7.0% Avg.
 Chlorides 8 – 16 ppm
 Water Extract Conductivity Microhms/cm 7.5 Avg.
 Standard Thickness, ± 7%Inches.
 Apparent Density, (Air Dry), ± 7%g/cc1.
 Weight, (Air Dry), ± 7%lbs./sq. ft..
 Tensile Strength, (Avg.)MD lbs./In.135195340500575700800
CMD lbs./In.25507585115140160
 Burst Strength, (Avg.)lbs./sq. in.120185320440510580625
 Tear Strength, (Avg.) gramsMD1802704756508751000 
 Dielectric Strength, (Avg.) grams AC, 25˚C (Avg.)volts/mil250250250250250250250

Click here to download the Kraft Insulation Spec Sheet.

Click here to download the Kraft Insulation SDS Sheet.

“Values shown are typical, are not guaranteed, nor to be used for specifications without approval.”

NOTICE: The above information and data are believed to be accurate and reliable. Windsor Stevens assumes no responsibility for end-use applications and no performance warranty is expressed or implied.