Mica Insulation: Types, Temperature Ratings, Uses and How to Specify It (2027 Guide)

Mica insulation is electrical and thermal insulation made from mica, a naturally layered silicate mineral that stays electrically insulating, arc-resistant and dimensionally stable at temperatures where glass-epoxy, polyester and other organic laminates have long since failed. Pressed into boards, sheets, rolls, tubes and gaskets, mica works continuously at 550 °C, 800 °C or 1100 °C depending on grade, with dielectric strength above 19.7 kV/mm and a UL 94 V-0 flammability rating.

This guide explains what mica insulation is, the three mica types, the product forms you can buy, where each one is used, how it compares with the alternatives, and how to specify and order it from Wedge Industries Limited in 2027.

What is mica insulation?

Mica is a group of sheet silicate minerals that cleave into thin, flexible, transparent flakes. Each flake is an almost perfect electrical insulator with very high dielectric strength, extremely low dielectric loss and no softening point below red heat. On its own a flake is small and fragile, so industry turns mica into two families of product:

• Natural sheet mica — blocks, splittings, strips, discs and washers cut straight from mined muscovite, used where a thin, clear, very high-dielectric piece is needed (gauge-glass shields, capacitor splittings, transistor washers).
• Mica laminates (micanite) — mica paper made from reconstituted flakes, impregnated with a binder and pressed under heat into rigid boards, thin plates, flexible sheets, rolls and tubes. A heat-stable silicone binder keeps the laminate working up to 1100 °C.

Mica is therefore unusual: it is both a high-voltage electrical insulator and a high-temperature thermal barrier in one material, which is why it dominates switchgear arc control, induction and arc furnace insulation and heating elements.

The three mica types: muscovite, phlogopite and synthetic

Choosing the right mica type is the first decision in any mica insulation specification.

Mica type	Colour	Continuous temperature (rigid board)	Choose it for
Muscovite (M)	Cream / ruby	550 °C	Best electrical and mechanical strength, lowest dielectric loss — switchgear, busbar supports, arc barriers
Phlogopite (P)	Amber-brown	800 °C	Higher heat resistance, softer to machine — induction furnaces, EAF / LF, smelting cells
Synthetic (fluorophlogopite, S)	White	1100 °C	Highest temperature index, dielectric strength and arc resistance — the most severe heat and arc duty

Typical literature values for the natural minerals: muscovite 500–600 °C maximum operating temperature, 40–80 kV/mm dielectric strength on 25–75 µm film, loss tangent 0.1–0.4 × 10⁻³, volume resistivity 4×10¹³ to 2×10¹⁷ Ω·cm; phlogopite 800–900 °C, 30–60 kV/mm, loss tangent 1–5 × 10⁻³, resistivity 10¹² to 10¹⁴ Ω·cm.

Mica insulation specifications

The table below gives typical values for WedgeMICA silicone-bonded rigid mica boards, taken from Technical Data Sheet WIL-TDS-MICA-001. They are typical test values rather than specification limits; batch values are reported on the Material Test Certificate with every delivery.

Property	WMB-M550 muscovite	WMB-P800 phlogopite	WMB-S1100 synthetic	Unit
Density	2250	2250	2250	kg/m³
Water absorption	0.35	< 1.0	< 1.0	%
Tensile strength (lengthwise)	195	110	110	MPa
Flexural strength (lengthwise)	166	NA	NA	MPa
Shear strength	207	207	207	MPa
Rockwell hardness	M70	M70	M70	—
Dielectric strength (minimum)	19.7	21.7	23.6	kV/mm
Breakdown strength (typical)	25	25	25	kV/mm
Arc resistance (minimum)	420	420	500	s
Relative temperature index	550	800	1100	°C
Flammability	V-0	V-0	V-0	UL 94

Full data for every grade is in the rigid mica board product page and the WedgeMICA catalogue (PDF).

Forms of mica insulation

Form	Grades	Thickness / size	Typical use	Product page
Rigid mica board / mica sheet	WMB-M550 · P800 · S1100	1–50 mm; 1000×1200 / 1000×2400 mm	Arc barriers, busbar supports, furnace panels, machined parts	Rigid mica board
Heater mica plate	WMH-M550 · P800 · S1100	0.15–1.5 mm; up to 1000×2400 mm	Heating elements, irons, toasters, air heaters	Mica heater plate
Flexible mica sheet	WMF-M500 · P600	0.15–5 mm; 1000×600 / 1000×1200 mm	Motor slot liners, coil wraps, transformers, breakers	Flexible mica sheet
Mica roll	WMR-GMG · GMP · GM · PM · CM	0.2–5 mm rolls or cut sheet	Slip plane between crucible and coil in induction furnaces	Mica roll
Mica tubes and bushes	WMT-M550 · P800 · S1100 · N130	ID from 8 mm; length to 1000 mm	Bolt, stud and terminal insulation in motors, furnaces, resistors	Mica tubes & bushes
Mica gasket sheet	WMG-P · WMG-PSS	Up to 3 mm	Exhaust, burner, turbine and heat-exchanger flanges	Mica gasket sheet
Natural muscovite mica	WMN-BLK · STR · DSC · FAB · GGS · TRW	Blocks, strips, discs, shields to size	Gauge-glass shields, capacitors, transistor washers	Natural muscovite mica
Machined mica parts	WMX-[grade]-[drawing]	To DXF / DWG / PDF drawing	Washers, rings, bushes, slotted coil supports, terminal plates	Machined mica parts

Where mica insulation is used

Switchgear and circuit breakers

Arc chutes, arc splitter plates, phase barriers and busbar supports see short bursts of arc plasma at several thousand degrees. Muscovite board (WMB-M550) gives the best combination of mechanical strength and 420 s arc resistance; synthetic board (WMB-S1100) is used where the arc duty is most severe.

Induction furnaces

Phlogopite board (WMB-P800) forms the coil supports, spacers and top and bottom panels, phlogopite tubes (WMT-P800) insulate the coil clamp bolts, and a glass- or ceramic-backed mica roll lines the coil as a slip plane. The roll protects the coil from refractory expansion, blocks leakage currents and makes the crucible easier to push out at relining.

Electric arc and ladle furnaces, smelting

Electrode clamp, mast arm, roof-lift and bus tube insulation on EAF and LF units, and busbar, anode clamp and cradle insulation in smelting pots and cells, are machined from WMB-P800 or WMB-S1100 board.

Heating elements and appliances

Thin heater mica plates carry the resistance wire in irons, hair dryers, toasters, kettles, ovens, air heaters and cylindrical resistance heaters. Grade follows element temperature: M550 below 550 °C, P800 below 800 °C, S1100 below 1100 °C.

Motors, transformers and coils

Flexible mica sheet wraps coils and lines slots in motors, generators and transformers, and mica tubes insulate studs and terminals. Mica tapes (glass, muscovite, phlogopite and synthetic) are used for fire-resistant cable and coil insulation.

High-temperature sealing

Phlogopite mica gasket sheet, plain or stainless-steel reinforced, seals exhaust, automotive, burner, turbine and heat-exchanger flanges that run too hot for rubber, fibre or graphite gaskets.

Boilers, batteries and electronics

Natural muscovite shields protect boiler water-level gauge glasses, thin splittings go into capacitors, and die-cut mica plates act as thermal runaway barriers between cells in EV and BESS battery packs.

Mica insulation vs the alternatives

Property	Mica board (WMB)	G10 / FR4 glass-epoxy	Ceramic fibre board	Calcium silicate board
Continuous temperature	550 / 800 / 1100 °C	about 130 °C	up to 1260 °C	650–1100 °C
Dielectric strength (min.)	19.7–23.6 kV/mm	19.7–21.7 kV/mm	Low — not an electrical insulator	Low — not an electrical insulator
Arc resistance (min.)	420–500 s	120–130 s	—	—
Flammability	UL 94 V-0	HB (G10) / V-1 (FR4)	Non-combustible	Non-combustible
Machinable to drawing	Yes, CNC	Yes	Limited	Yes
Best for	Heat + voltage + arcing together	Ambient-temperature panel parts	Furnace thermal lining	Structural fire and heat insulation

The rule of thumb: use glass-epoxy where the part stays below 130 °C and never sees an arc; use ceramic fibre or calcium silicate where you need thermal insulation but not electrical insulation; use mica where the part must insulate electrically and survive heat, arcing or molten-metal radiation. For thin, very low thermal conductivity layers next to an electrical barrier, aerogel is often paired with mica in battery packs.

How to cut, machine and install mica insulation

1. Saw, CNC route, drill, mill, turn and tap rigid board with carbide tooling; use sharp tools and moderate feed to avoid edge delamination, and back the sheet with a sacrificial board when drilling.
2. Cut flexible sheet and heater plate with shears or a knife, or have parts stamped to drawing.
3. Machine under local dust extraction and wear an FFP2 / P2 mask, safety glasses and gloves — natural mica can carry traces of crystalline silica.
4. Ventilate during the first heat-up above about 300 °C, when a little binder burns off as light smoke.
5. Store sheets flat, indoors and dry, in the original packing, away from heavy point loads; shelf life is unlimited when stored this way.

For production quantities, order machined mica parts finished to drawing so your line never handles raw sheet or mica dust.

Mica insulation price and how to order (2027)

Mica insulation is priced by mica type, thickness, sheet size or drawing and quantity, so Wedge Industries Limited quotes each enquiry in ₹ INR and $ USD rather than publishing a list price. Synthetic mica costs more than phlogopite, which costs more than muscovite; thin heater plates and flexible sheets are priced per sheet, rigid boards per sheet or per kg, and machined parts per piece against the drawing.

Order by SKU — family-grade-thickness (mm)-size, with size codes 1006 = 1000×600, 1012 = 1000×1200, 1024 = 1000×2400 mm and CUT = cut to drawing. Example: WMB-P800-10-1012 is a 10 mm phlogopite rigid board, 1000 × 1200 mm. MOQ and lead time are confirmed with each quotation, sample pieces are available for approval before bulk orders, and export orders ship flat-packed on pallets or in wooden cases to 45+ countries.

Get PriceDownload the WedgeMICA catalogue (PDF)

Mica insulation FAQs

Related mica insulation products

• Electrical insulation — materials, ratings and the full Wedge product range (2027 guide)
• Mica insulation — full WedgeMICA range and selection guide
• Rigid mica board / mica sheet (550 / 800 / 1100 °C)
• Mica heater plates · Flexible mica sheet · Mica roll for induction furnace
• Mica tubes & bushes · Mica gasket sheet · Natural ruby muscovite mica · Machined mica parts
• Wet ground mica powder · High-temperature insulation · Aerogel for BESS