Soft Mica Sheets are made by mica material mixed with proper adhesive, then pressed and baked into flat sheet. Under normal conditions the sheet remains soft and heat-resistant, and delivers the best and most reliable permanent sealing characteristics available in a mica sheet product. Soft mica sheet is the standard choice where the flange cannot take a high bolt load, where the joint gap opens and closes with temperature, and where the seal must not stick or burn onto the flange face.
The figures below cover the five parameters that decide whether this sheet will fit your joint. Confirm the exact grade and tolerance on the enquiry.
Custom gaskets are cut to drawing on request. Send us the outer diameter, inner diameter, bolt circle, thickness and quantity and we will confirm the achievable tolerance and price before quoting.
These four features are what make soft mica sheet the correct choice in joints where other gasket materials fail. Each is listed with its practical benefit on the flange.
Low minimum compression load
Seals even when the flange cannot take a high bolt load — critical on glass-lined vessels, plastic flanges, cast iron housings and older equipment where bolt load is limited by the flange design.
Self-adjusting to enlarging gaps
As the joint gap opens and closes with temperature, the soft sheet expands and contracts with it — keeping the seal tight through thermal cycling. No burning and no sticking to the flange face.
Compensating action in ceramic and steel joints with unequal expansion
Ceramic and steel expand at very different rates under heat. A rigid gasket would leak as soon as the joint opens. Soft mica sheet takes up the differential movement and keeps the seal intact — this is where soft mica sheet outperforms almost every other sealing material.
Best and most reliable permanent sealing characteristics
The sheet holds its sealing performance over time — it does not harden, does not lose its compressibility and does not stick to the flange face. The joint can be reopened without damaging the sealing surface.
Soft mica sheet is used in three main ways. Each is listed below with the reason it is the right choice.
Cut Into Gaskets
The sheet is soft and easy to cut with standard workshop tools. Custom gaskets can be produced to drawing for any flange configuration or equipment closure.
Filler for Spiral Wound Gaskets
Soft mica sheet is used as the soft filler between the metal windings of a spiral wound gasket — providing the compressible sealing layer that closes the joint.
Permanent Sealing Layer
For high-temperature flanges, ceramic-to-steel joints and process equipment where the seal must survive both heat and differential thermal expansion over a long service life.
Both are made from mica, but they are made with different adhesive levels and different pressing pressures, so they behave very differently in service.
Soft mica sheet — sealing priority
Compressible and flexible. Conforms to flange surfaces at low bolt load. Self-adjusts to changing gaps. The right choice when sealing is the priority and the joint must stay tight through thermal cycling.
Hard mica sheet — rigidity priority
Denser and stiffer. Holds its own shape and supports a load. The right choice when the sheet is used as an insulation board — furnace construction, element supports, insulation barriers — and rigidity matters more than compressibility.
Choose soft when…
The flange cannot take a high bolt load; the joint gap opens and closes with temperature; the seal is in contact with ceramic or glass; the gasket must not stick to the flange face; or the gasket is being cut from sheet for a specific flange geometry.
Choose hard when…
The sheet is a load-bearing insulation board; the sheet must hold its shape at high temperature; the sheet is used as a furnace lining or an electrical insulation barrier; or the sheet is part of a structural assembly.
Q.01What is a soft mica sheet used for?
Soft mica sheet is used as a compressible high-temperature sealing material. It is cut into various gaskets for flanges and process equipment, used as the filler for spiral wound gaskets, and forms a permanent sealing layer in ceramic and steel joints that have unequal thermal expansion. It delivers the best and most reliable permanent sealing characteristics available in a mica sheet product.
Q.02What is the difference between soft mica sheet and hard mica sheet?
Soft mica sheet is made with a higher proportion of adhesive and a lower press pressure, giving a compressible, flexible material that conforms to flange surfaces at low bolt load. Hard (rigid) mica sheet is denser and stiffer, and is used as an insulation board where the sheet must hold its shape and support a load. Soft mica sheet is the right choice when sealing is the priority; hard mica sheet is the right choice when rigidity is the priority.
Q.03What are the technical parameters of KXT-B501?
Sheet sizes: 1000 × 1200 mm and 600 × 1000 mm. Thickness: 0.5–5.0 mm. Temperature resistance: 650–900 °C. Pressure: 10 MPa. Density: 1.8–2.1 g/cm³. The sheet is soft and heat-resistant under normal conditions, and provides low minimum compression load, self-adjusting behaviour on enlarging gaps, and no burning or sticking to flanges.
Q.04Why use soft mica sheet instead of a standard gasket material?
Soft mica sheet is chosen where other gasket materials fail. It has a low minimum compression load, so it seals even when the flange cannot take a high bolt load. It self-adjusts to enlarging gaps, so it keeps sealing as the joint opens with temperature. It does not burn or stick to flanges, so the joint can be reopened without damage. And it compensates for unequal expansion in ceramic and steel joints, where the two materials expand at different rates and a rigid gasket would leak.
Q.05What is the maximum temperature and pressure?
The service temperature range for KXT-B501 soft mica sheet is 650–900 °C, and the maximum pressure is 10 MPa. Do not operate at the maximum temperature and maximum pressure simultaneously. Confirm the exact grade for your application on the enquiry.
Q.06Can you cut soft mica sheet into a gasket for me?
Yes. Soft mica sheet is easy to cut and can be supplied as full sheets or as finished gaskets cut to your drawing. Send us the outer diameter, inner diameter, bolt circle, thickness and quantity and we will confirm the achievable tolerance and price before quoting.
Tell us the sheet size (1000 × 1200 mm or 600 × 1000 mm), the thickness (0.5–5.0 mm), the continuous operating temperature and pressure, and the quantity. If you need cut gaskets, send the drawing with the outer diameter, inner diameter, bolt circle and tolerance. If you are replacing an existing soft mica sheet, send us the current specification and we will match it.
