representing Hokuetsu Toyo Fibre Co., Ltd. in the USA

What is Vulcanized Fibre?

Vulcanized fibre is a material manufactured by gelatinizing several plies of high purity cellulose papers. It has extremely high internal bond strength, and mechanically excellent punching, forming, machining and many other unique properties. Hokuetsu Toyo Fibre proudly carries specialty grades to comply any application required by users, such as water resistant grades, flame retardant grades, combination grades etc. in roll, sheet and coil.

Vulcanized Fibre Revisited, Electrical Insulation and A Whole Lot More

By Robert A. Zembower

Vulcanized Fibre is a laminated plastic composed of only one ingredient: natural cellulose. One of the first "plastics" ever developed, Vulcanized Fibre is a tough, resilient, "hornlike" material that is lighter than aluminum, tougher than leather, stiffer than most thermoplastics.

Developed in the early 1870s by passing 100% cotton paper through an acid bath, Vulcanized Fibre enabled the growth of the electrical and automotive industries, while substantially contributing to the development of modern sporting equipment, railroads, textile manufacturing, welding, and many others.

Fibre offers flexibility, impact resistance, high tear strength and a smooth, abrasion resistant surface. It can be machined, punched, slit, threaded, formed, molded and wound into tubes for literally countless applications. It provides excellent electrical insulation values, and is arc and track resistant. Even though composed of cotton and wood pulp, standard VF can be used at operating temperatures of 110C-120C and has a flame resistance rating of U.L. 94HB. The use of additives and/or coatings can provide a rating of 94VO, and laminating to polyester film will bring the U.L. thermal rating up to 130C.

Vulcanized Fibre is impervious to most organic solvents, oils, and petroleum derivatives. This makes it an excellent choice for use in oil. Like wood, to which it is related, VF will absorb water, but will not delaminate in its presence. It will tend to "breath" or adjust its moisture content as the ambient moisture level changes.

As a tribute to its tremendous physical strength, Vulcanized Fibre is the substrate of choice for heavy sanding discs. VF has been used for these abrasive discs since they were first developed. The application requires a backing that is tough, flexible and tear resistant to withstand 20,000 RPMs while in direct contact with rough steel welds. Here a loose piece of material becomes a dangerous projectile and a weak backer leads to excessive downtime.

The newer wood laminating grade of vulcanized fibre strengthens wood laminations used in skis, skateboards, support beams and as a sub-laminate under thin wood veneers.

Vulcanized Fibre is produced in at least 5 distinct grades:

  • Commercial Grade; standard gray, black or red, used for many applications such as washers, gaskets, gears, handles, etc.
  • Electrical Grade: high dielectric gray, 100% cotton, very flexible, (historically called "fish-paper"), this grade is suitable for layer and ground insulation and has variations including "top-stick" grade used for wedges in small motors.
  • Trunk Fibre: Tough and abrasion resistant; used to surface steamer trunks, drum cases, wear and skid panels.
  • Bone Fibre: Exceptionally hard and dense, used for tight machining, tubing, pool cue ferrules (tips), cut out fuses.
  • Wood Laminating: Tough, multi-directional tensile and torsion strength, provides support and strength wherever wood laminations are used, particularly used under thin and exotic veneers as a stabilizer/strengthener.
  • Vulcanized Fibre as rag paper

    Thinner gauges of electrical grade Vulcanized Fibre, being composed of 100% cotton rag, has been recognized by U.L. as rag paper. Vulcanized Fibre can be substituted for any other versions of 100% cotton rag paper in U.L. recognized electrical insulation systems, including where laminated to polyester films, or adhesive or b-stage coated.

    Vulcanized Fibre is unique in that it is a thermoset material that acts thermoplastic when exposed to temperatures above 350F or subjected to steam. Under these conditions it can be formed or molded, stretched or compressed. The plasticity of wet fibre allows it to stretch 25% during molding, or compressed by 50%. Discs of Fibre have been molded into helmets, but more common applications find it shaped into strong angles, channels and rods for supports. It can also be corrugated to allow cooling air and oil to flow in electrical apparatus.


    • Tensile Strength, psi 6,000-12,000
    • Flexural Strength, psi 12,000-20,000
    • Compressive Strength, psi 20,000-30,000
    • Shear Strength, psi 11,000-15,000
    • Impact Strength, ft/lbs per in. 4-8
    • Rockwell Hardness R60-R100
    • Density, gm/cc 1.1-1.3
    • Dielectric Strength, vpm 150-400
    • Power Factor, 1000kc .03-.08
    • Dielectric Constant 4-7
    • Water Absorption, 2hr,1/8",% 15
    • Thermal Conductivity, Btu/hr/sqft/F/in 3

    How moisture affects fibre:

    Moisture is to fibre what heat is to metal. Normal moisture content (at typical ambient temperature/humidity ranges) is 5%-8%. This amount of moisture in fibre contributes to its resilience, punching and forming capabilities. Water softens or plasticizes it. In use, moisture can cause dimensional changes and should be protected against via a coating. Again, most of these effects can be minimized or eliminated through proper application selection and a quick water resistant coating.

    In more modern times, Vulcanized Fibre offers advantages sought more today than historically.

    1. First, Vulcanized Fibre is produced from cotton cloth cuttings, primarily blue jeans, and makes good use of materials that would otherwise be thrown into the landfill. In this way, Vulcanized Fibre is one of the original products of effective recycling. In fact, the quest is now on to find an appropriate use for Vulcanized Fibre trim and scrap (possibly as a furnace fuel).
    2. Secondly, since VF is 100% natural product, it produces no harmful out-gassing during machining, like phenolics and other plastics, and the trim can be disposed of in standard trash receptacles.
    3. Third, Electrically, vulcanized fibre exhibits outstanding resistance to arcing and tracking. Decomposition products of carbon dioxide and water actually work to quench the arcing.

    Vulcanized Fibre, the first manufactured plastic, one of the first electrical insulations, "oft forgotten but never obsolete". Vulcanized Fibre continues to provide utility in a variety of electrical and mechanical applications.


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