Silicone systems for extreme usage conditions

SONDERHOFF FERMASIL is the two-component silicone system for the manufacturing of soft elastic silicone elastomers and silicone foam sealings for extreme usage conditions.

Using FIPFG dispensing technology (Formed-In-Place-Foam-Gasket), SONDERHOFF FERMASIL is applied directly to the part and cures there at room temperature.

Chemical constituents

The systems consist of an A-component and a cross-linking B- component, which are mixed with each other in a  redetermined mixing ratio. After mixing the components, most systems react by their own at room temperature and generate a soft elastic silicone foam sealing or permanently elastic silicone elastomers.

SONDERHOFF FERMASIL is processed using low pressure mixing and dosing machines for two components. Suited for silicone sealants re dynamic or static mixing systems. Henkel recommends dynamic mixing systems for increased ease of material processing.

SONDERHOFF FERMASIL can be used at a constant temperature from -60 up to +180°C and for a short time up to +350°C, while maintaining its softness and flexibility at any time. Due to its closed cell structure, SONDERHOFF FERMASIL does not absorb water and is suitable for use in tropical or damp environments. It is also highly resistant to other chemicals (e.g. commercial cleaning agents, alcohols, diluted acids and lyes, brake fluids, and cooling agents).

Henkel can draw on the variety of more than 200 application- specific formulations of the SONDERHOFF FERMASIL product family.

Physical and chemical Properties*
Appearance White, grey or black, other colors upon request (also transparent)
Hardness Gel-like up to  Shore A possible
Compression load deflection (25% compression) From 20 to 150kPa (at 25% compression)
Density From 0,25 g/cm³ to 2 g/cm³
Temperature resistance From -60° C to +180° C (temporary up to +350° C)
Tensile strength Up to 4,5 MPa [N/cm²]
Elongation at break Up to 600 %
Compression set (DVR) Greater than 97 % (depending on test conditions)
Water absorption < 1 %
Flame retardancy Up to UL-94 HF-1 possible
Viscosity of the A component: from 1.000 mPa·s (liquid) to 250.000 mPa·s (highly pasty)
Optional features
E.g. UL50 conformity, UV resistant, ingress protection class up to IP 69K and NEMA 4-6p 
(achievable with suitable component design), good chemical resistance

Broad spectrum of characteristics of SONDERHOFF FERMASIL

Depending on customer requirements, SONDERHOFF FERMASIL ystems can express many different characteristics. Different part applications are protected effectively in extreme surroundings. Numerous SONDERHOFF FERMASIL product family recipes are available for this..

High temperatures

The different softness grades and flexibilities of SONDERHOFF FERMASIL silicone systems are maintained even at long-term temperatures of -60 to +180°C, in special cases to 250°C, and for short periods even to +350°C.

Very low water absorption (<1%)

Because of the closed-celled structure of silicone foams, they are tropicalised and wet room safe; infiltration protection to IP 69K and NEMA 4-6p are possible.

High chemical resistance

SONDERHOFF FERMASIL silicone systems are resistant to many chemicals (e.g. Common cleaning materials, alcohols, dilute acids and alkalis, brake fluids, oils and lubricants, coolants) and are low-fogging.


Ease of flow, reactivity and colour can be multifariously varied.

Curing at room temperature

SONDERHOFF FERMASIL silicone foams cure on the component at room temperature in a time range from approx. 20 minutes to around 12 hours, becoming a soft foam seal. The part can then be sent on to further processing.

Crystal clear or translucent silicone potting

Temperature stable to 180°C, very high tear resistance and flexural strength (example extension at break 600%), UV-stable

Flame protection in accordance with UL 94 HF-1

SONDERHOFF FERMASIL silicone systems can be equipped with UL 94 HF-1 flame protection; any flame after this is extinguished within 10 seconds, with max. 30 seconds’ afterglow.

ATEX approval

For SONDERHOFF FERMASIL silicone foam seals, an ATEX approval for component applications in explosive environments e.g. mining, oil drilling is possible.

FERMASIL® – the technology

SONDERHOFF FERMASIL sealing foams can be efficiently and accurately piped onto parts from the most varied of branches of industry using the FIPFG (Formed-In-Place Foam Gasket) technology and mixing and dispensing systems by Sonderhoff. Depending on the viscosity, they are either freely applied to the surface of the part as a paste or poured in fluid form into a groove.

The exact interplay of the most variable set-up parameters and additional functions of the mixing and dispensing machines, the exact calibration of the part and SONDERHOFF FERMASIL foam seal within the complete construction and the right material choice ensure truly secure sealing of industrial components for the most varied uses against damp, dust and other environmental influences is achieved.



SONDERHOFF FERMASIL – the reaction process

The chemical reaction of SONDERHOFF FERMASIL sealing foams is initiated by mixing the A- and B-components. The applied compound foams up to a uniform gasket under room temperature conditions.

SONDERHOFF FERMASIL – The foaming process
Pot life: The time span from the mixing of the A- and B-components to the beginning of the foaming time (approx. 5 – 60 sec.). It is also referred to a processability time or service life.
Foaming-up time: The time span in which the SONDERHOFF FERMASIL foam system expands to form a sealing body (after approx. 1 – 20 min.).
Tack-free time: The time from which the sealant surface of SONDERHOFF FERMASIL foam systems can be touched without causing damage (after approx 2 - 60 minutes)
Assembly time:

The chemical reaction has progressed so far that the SONDERHOFF FERMASIL foam systems can bear loads or the foamed components can be assembled (after approx. 30 minutes - 12 hours)



The SONDERHOFF FERMASIL offers effective component protection for the most diverse requirements for sealing, gluing and potting. In the table you will find a selection of different silicone systems for various industries, from lighting to control cabinet and automotive construction, to electronics, packaging and white goods.

Designation Application* Viscosity
Shore 00
Other properties  


Distance sensors

8.000 80
Shore 00
0,65 Slightly foamed, liquid silicone system, particularly suitable for ultrasonic sensors – good ratio between resonance and absorption behavior  


Drive belt cover

> 100.000 65 Shore 00 0,35 Highly viscous, stable, medium hardness, curing possible without heat treatment  


Underbody cover

25.000 35 0,30 Extremely soft, semi-thixotropic, good processability  


Maintenance cover Ad-Blue

45.000 45 0,25 Soft, semi-thixotropic, good price-performance ratio  



100.000 60 0,30 Thixotropic, medium hardness  


Luminaires, E-boxes, packaging, switch cabinets

approx. 15.000 55
Shore 00
0,30 Liquid, good flow, curing possible without heat treatment, for lighting with ATEX approval  


Lighting with ATEX approval

50.000 40 0,25 Soft, semi-thixotropic, good price-performance ratio  


Potting of electronics, battery packs, sensors, PC boards

5.500 40 Shore A 1,00 Very good dielectric properties, good flow rating, color and reactivity adjustable, also able to process gel-like  


Food boxes, packaging covers in contact with food

approx. 15.000 35-50 Shore A 1,15 Fast curing, good mechanical properties  


Switch cabinets, E-boxes, ultrasonic sensors

approx. 8.000 60
Shore 00
0,35 Liquid, PTB approved in electric enclosure applications  
47-14 Enclosures > 100.000 60
Shore 00
0,35 Thixotropic, stable, standard material with medium hardness, UL-50E listed  


Switch cabinets with ATEX approval

> 100.000 60
Shore 00
0,35 UL50E listed, thixotropic, stable, curing possible without heat treatment  
3590-2-DG Enclosures 80.000 40 0,30 Soft, thixotropic, fast curing  
38C3-1 Enclosures > 100.000 40 0,35 Soft, thixotropic, stable  


Good reasons for using SONDERHOFF FERMASIL


  • ... can be used at a constant temperature up to +180°C, for special types up to +250°C
    and temporary up to +350°C.
  • … keeps the greatest possible flexibility even down to -60°C.
  • … is closed-cell and therefore nearly do not absorb water.
  • … is highly resistant to many chemicals.
  • … is hydrolysis stable and therefore suitable for use in tropical or damp environments.
  • … is tack-free in 2– 60 minutes, depending on the thermal conditions. A furnace can significantly
    shorten the reaction time, but it is not always necessary.
  • … is processed using a mixing and dosing machine for two components and can be adapted flexibly
    and quickly to other parts for sealing application at any time.
  • … develops a cross-linked structure which is extremely resistant to environmental effects
    such as humidity, dust and temperature.
  • … has an exceptional long-term behavior and almost 100% resetting ability, even after many years
    of continual use.
  • … is in some cases also suitable for direct contact with food.