High-Temperature Resistant Felts
High-temperature felts by Alkegen – Insulfrax® to 1200 °C, Durafelt® HD to 1250 °C, Durafelt® Z to 1400 °C.
SENN supplies high-temperature resistant felts in three different material lines from Unifrax / Alkegen: Insulfrax® felt as a bio-soluble, REACH-compliant alkaline earth silicate wool up to 1200 °C, Fiberfrax® Durafelt® HD as a classic high-strength aluminium silicate felt up to 1250 °C and Fiberfrax® Durafelt® Z as a zirconium oxide-stabilised premium variant up to 1400 °C. Each line is available in different sheet sizes and thicknesses - including original data sheets for download.
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Advantages at a glance
- Three material lines for temperatures from 1200 °C to 1400 °C
- REACH-compliant organic line (Insulfrax®, alkaline earth silicate wool)
- High-strength RCF line (Fiberfrax® Durafelt® HD, tensile strength > 100 kPa)
- Zirconium oxide stabilised up to 1400 °C (Fiberfrax® Durafelt® Z)
- Thicknesses from 3 mm to 30 mm - customised cuts also possible
- Original data sheets for download directly on this page
- Advice & design by SENN as authorised sales partner
Typical applications
- High-temperature gaskets for furnace doors, flaps and flanges
- Linings for moulds and casting channels
- Back insulation in molten metal transfer systems
- Filling material for expansion joints in industrial furnaces
- Heat protection and sound insulation in the automotive sector (exhaust gas, turbochargers)
- Insulation of induction furnaces and crucibles
- Thermal insulation for reactors, turbines and waste heat boilers
Three material lines in comparison
The three felt lines cover different requirement profiles: Insulfrax® is the preferred regulatory choice for the EU market, Durafelt® HD offers the highest tensile strength for mechanically stressed applications, and Durafelt® Z achieves the highest operating temperatures as a zirconium oxide-stabilised premium variant.
Feature Insulfrax® Filz Fiberfrax® Durafelt® HD Fiberfrax® Durafelt® Z Fibre family AES (bio-löslich) RCF (Aluminiumsilikat) RCF + ZrO₂ Classification temperature 1200 °C 1250 °C 1400 °C Melting point > 1330 °C 1800 °C 1740 °C Raw density 170 – 270 kg/m³ 200 – 300 kg/m³ 200 – 300 kg/m³ Tensile strength > 50 kPa > 100 kPa > 50 kPa Thermal conductivity @ 1000 °C 0,20 W/m·K 0,19 W/m·K 0,21 W/m·K Available thicknesses 6 – 25 mm 3 – 25 mm 3 – 30 mm REACH status compliant (bio-soluble) RCF (CMR Cat. 2) RCF (CMR Cat. 2) Insulfrax® felt - the bio-soluble line
Insulfrax® felt is made from Insulfrax® alkaline earth silicate wool (AES) - a bio-soluble fibre based on calcium magnesium silicate. In contrast to classic refractory ceramic fibre (RCF), Insulfrax® is REACH-compliant and not classified as a CMR substance. The fibre dissolves in the lung fluid test within a few days.
Chemical analysis: SiO₂ 61-67 %, CaO 27-33 %, MgO 2.5-6.5 %, Al₂O₃ < 1 %, Fe₂O₃ < 0.6 %.
Thermal conductivity: 0.08 W/m-K at 400 °C, 0.10 at 600 °C, 0.15 at 800 °C, 0.20 at 1000 °C. Available in sheet sizes 1000 × 610 mm and 1250 × 1000 mm in thicknesses of 6, 9, 12, 18 and 25 mm.
Recommended for: Standard applications in the EU market where REACH conformity is required or advantageous - high-temperature seals, mould linings, back insulation in melting plants, joint seals.
Fiberfrax® Durafelt® HD - the high-strength RCF line
Fiberfrax® Durafelt® HD is a classic aluminium silicate felt made from refractory ceramic fibres (RCF). With a tensile strength of over 100 kPa, the line offers the highest mechanical strength of the three variants - ideal for applications in which the felt is under tension or bending.
Chemical analysis: SiO₂ 50-58 %, Al₂O₃ 42-50 %, alkalis < 0.25 %.
Thermal conductivity: 0.11 W/m-K at 600 °C, 0.14 at 800 °C, 0.19 at 1000 °C. Melting point 1800 °C, classification temperature 1250 °C. Available in rolls (width 610 or 1220 mm) and as sheets 1250 × 1000 mm in thicknesses from 3 to 25 mm.
Recommended for: mechanically stressed high-temperature gaskets, mould linings with high handling requirements, applications outside the EU or where RCF is required for process-related reasons.
Fiberfrax® Durafelt® Z - the premium version with zirconium oxide
Fiberfrax® Durafelt® Z is the zirconium oxide-stabilised premium version of the Durafelt® range. With a classification temperature of 1400 °C, it achieves the highest application temperatures of all three felts. The ZrO₂ content of 14-18 % improves volume stability at very high temperatures.
Chemical analysis: SiO₂ 52-56 %, Al₂O₃ 28-32 %, ZrO₂ 14-18 %, alkalis < 0.25 %.
Thermal conductivity: 0.15 W/m-K at 800 °C, 0.21 at 1000 °C, 0.29 at 1200 °C. Melting point 1740 °C. Available as sheets 1250 × 1000 mm in thicknesses of 3, 6, 9, 12, 18, 25 and 30 mm - the only line with 30 mm thickness available.
Recommended for: High-temperature applications above 1250 °C up to a maximum of 1400 °C, when neither Insulfrax® nor Durafelt® HD reach the required temperature class.
Original data sheets for download
The official manufacturer data sheets for all three material lines are available for direct download:
Note: REACH and CMR classification
Refractory ceramic fibres (RCF) - the fibre base of Fiberfrax® Durafelt® HD and Z - are classified as CMR Cat. 2 (suspected carcinogenic) in the EU. For many standard applications, the bio-soluble Insulfrax® line is the preferred regulatory choice. When using RCF products, the instructions in the relevant safety data sheet and personal protective equipment must be observed. We will be happy to advise you on which line is the right one for your application.
Frequently Asked Questions
Which of the three felts is REACH-compliant?
Insulfrax® felt is the REACH compliant choice. The fibre consists of bio-soluble alkaline earth silicate wool (calcium magnesium silicate) and is not classified as a CMR substance. The two Fiberfrax® Durafelt® lines (HD and Z) are classic refractory ceramic fibres (RCF) and are subject to CMR category 2.
What is the difference between Durafelt® HD and Durafelt® Z?
Durafelt® HD is the classic aluminium silicate variant with maximum tensile strength (> 100 kPa) and a classification temperature of 1250 °C. Durafelt® Z is zirconium oxide-stabilised (14-18 % ZrO₂) and achieves a higher classification temperature of 1400 °C, but has a lower tensile strength (> 50 kPa). HD is selected when mechanical stress is the main focus; Z when the maximum application temperature is decisive.
What thicknesses and panel sizes are available?
Insulfrax® felt: 6 / 9 / 12 / 18 / 25 mm in sheet sizes 1000 × 610 mm and 1250 × 1000 mm. Durafelt® HD: 3 / 6 / 9 / 12 / 18 / 25 mm as rolls (width 610 or 1220 mm) and sheets 1250 × 1000 mm. Durafelt® Z: 3 / 6 / 9 / 12 / 18 / 25 / 30 mm as sheets 1250 × 1000 mm. Other thicknesses and special formats on request.
How do I choose the right felt for my application?
The choice depends on three factors: Application temperature (up to 1200 °C → Insulfrax®, up to 1250 °C → Durafelt® HD, up to 1400 °C → Durafelt® Z), regulatory requirements (REACH/CMR → Insulfrax® preferred) and mechanical load (highest strength → Durafelt® HD). For combined requirements, please contact our technical office.
Does SENN also offer customised cuts or other thicknesses?
Yes, special cuts from the standard sheets and non-listed thicknesses are available on request and subject to a minimum order quantity. We also supply ready-made gaskets and die-cut parts from all three felt lines. Send us your drawing or specification - we will check availability and price at short notice.
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Since 2001, KS Kneissl & Senn Technologie GmbH
has been producing insulation materials and seals for a wide range of applications up to a temperature range of 1600 °C. A diverse range of machinery (CNC 5-axis milling, plotting, punching, sewing, water jet cutting, vacuum forming, etc.) enables us to shape a wide variety of materials for you. The main materials include: glass fibers, aramid fibers, mineral fibers, biosoluble fibers, ceramic fibers, silicate fibers, vermiculite, calcium silicate, microporous materials, elastomers (rubber, silicone, silicone foam, etc.), etc.
The company has been ISO9001 certified since 2009, currently in accordance with the 2015 revision of the standard.
