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HELISOL®:
The next generation of heat transfer fluids

In the world of high-performance production and solar innovation, heat is both a vital resource and a constant challenge. Systems must run reliably at extreme temperatures, deliver maximum efficiency and meet strict environmental standards. This calls for advanced heat transfer solutions – such as HELISOL®, our silicone-based heat transfer fluid engineered to perform where conventional fluids reach their limits.

HELISOL® heat transfer fluids are highly stable silicone fluids specifically designed for high-temperature and heating/cooling applications. They are used in industrial heat transfer, concentrated solar power (CSP) and solar heat for industrial processes (SHIP) – wherever reliable thermal control is essential. Across all these applications, the advantages remain the same: unmatched thermal stability across a wide temperature range, long-term reliability and safety.

From −40 °C to +425 °C: one fluid, full range

Operating temperature range of HELISOL® heat transfer fluids

HELISOL® heat transfer fluids offer exceptional thermal stability across an unmatched temperature range – from -40 °C to +425 °C – without the need for trace heating or freeze protection. Whether a system starts up in sub-zero climates or operates continuously at peak thermal loads, HELISOL® fluids maintain their integrity, resisting fouling and sludge formation.

In practice, that means fewer fluid changes, less maintenance effort and greater operational flexibility – one fluid that performs consistently across all seasons and applications.

Heat? Cold? Always stable!

As shown by a test from our laboratory: after nearly six months at 425 °C, the silicone fluid (left) remains stable, while the organic heat carrier (right) already begins to decompose at 400 °C and must be replaced. Otherwise, the resulting solid residues could damage heat exchangers or pumps.

HELISOL® heat transfer fluids compared to organic heat carriers


HELISOL® heat transfer fluids operated at 425 °C


Organic heat carrier operated > 400 °C

Safe for people and processes

In many applications, aromatic hydrocarbons are still frequently used as heat transfer media. However, most of these substances have now been classified as CMR (carcinogenic, mutagenic or reprotoxic), which involves extensive safety precautions and documentation.

HELISOL® silicone fluids, by contrast, are based on polydimethylsiloxanes and contain no hazardous ingredients when supplied. They can be handled and operated safely without special protective measures, offering peace of mind for both operators and the environment.

HELISOL® combines safety and performance – offering a modern, sustainable alternative to conventional aromatic or mineral-oil-based fluids.

HELISOL®:
The safer choice for industrial heat transfer

Industrial systems demand reliability, safety and efficiency. HELISOL® heat transfer fluids deliver all three – with unmatched thermal stability and a broad operating range. With minimal fouling and less hazardous ingredients during operation, HELISOL® ensures long-term reliability and safety, making it the smart choice for industries that process chemicals, polymers and metals.

Seamless transition: how Nünchritz switched to HELISOL®

Change can be daunting, especially in complex industrial environments. But at our Nünchritz polymer plant, the move from an organic heat transfer fluid to HELISOL® was a textbook success. After draining and flushing several kilometers of pipeline, the silicone fluid was added. Only two days later, production was running smoothly again. The result: immediate operational stability, no need to adjust valves or operating parameters, and a significant reduction in maintenance.

A textbook transition and a complete success, as process engineer Jan Lauschke sums up: “We should have made the switch much earlier. It’s a real game-changer for efficiency and compliance.”

  • A smart fluid for smart factories: based on silicone chemistry, HELISOL® ensures minimal fouling, low maintenance and a long service life – perfect for industries seeking precision, durability and reliability.
  • No freeze, no fuss: With a low pour point and wide temperature range, HELISOL® keeps facilities running smoothly even in extreme cold, ensuring continuous operation and energy efficiency all year round.
  • Superior to conventional fluids: HELISOL® resists degradation and fouling. Proven in safety and performance trials, it offers a cleaner, safer and more sustainable solution for modern industrial heat transfer.

HELISOL® in CSP systems:
Unlocking the future of solar heat

With its wide operating range, low hydrogen formation, and superior thermal stability, HELISOL® is the ideal fluid for concentrated solar power (CSP) applications. Unlike most organic fluids, HELISOL® is recyclable and delivers high performance with reduced maintenance downtime – helping operators achieve their sustainability goals without compromising efficiency or reliability.

In the solar field of CSP systems, HELISOL® circulates through receivers – steel tubes enclosed by vacuum-insulated glass tubes to prevent heat loss.

Advantages at a glance

  • More energy with less risk: Safe and stable at high temperatures, HELISOL® is ideal for CSP systems where safety and uptime are critical. It withstands film temperatures up to 450 °C without degradation.
  • Minimized heat loss, maximized output: With low fouling and high thermal stability, HELISOL® enhances energy conversion efficiency in solar thermal plants. It minimizes heat loss and maximizes output, ensuring a stronger return on investment.
  • Designed for parabolic troughs and Fresnel systems: In either system, HELISOL® delivers consistent performance and minimal degradation, ensuring reliable solar-energy generation day after day.
  • Handles the heat – up to 425 °C: HELISOL® thrives in high-temperature solar environments, outperforming organic fluids that degrade under thermal stress.

HELISOL® in SHIP applications:
Delivering clean steam from solar heat

In solar heat for industrial processes (SHIP) systems, HELISOL® efficiently transfers solar energy to generate process steam – safely and sustainably. It enables the decarbonization of industrial heat without compromising reliability or performance. That’s clean energy with industrial-grade efficiency.

Advantages at a glance:

  • A smart step toward sustainable manufacturing: HELISOL® helps industries decarbonize by integrating solar heat with minimal risk and maximum reliability. Its recyclable nature supports ESG goals while maintaining operational excellence.
  • No fouling. No shutdowns. Just steam. HELISOL® keeps SHIP systems running smoothly, reducing costly interruptions. Unlike organic fluids, it does not form sludge or light ends – meaning more uptime and fewer surprises.
  • Works in cold starts and on hot days: HELISOL® performs across the full temperature spectrum – no trace heating required. Its wide operating range ensures consistent steam generation, even under fluctuating conditions.
  • Designed for the sun, built for efficiency: HELISOL® fluids deliver high thermal stability up to 425 °C and excellent low-temperature behavior down to –40 °C. With reduced hydrogen formation and no need for freeze protection, they extend receiver life and boost plant uptime.

FAQs about HELISOL® heat transfer fluids

HELISOL® heat transfer fluids are linear, clear, odorless and non-reactive polydimethylsiloxanes with a viscosity range of approx. 5 to 35 mm2/s at room temperature.

Due to their chemical structures, HELISOL® heat transfer fluids have an outstanding property profile, which sets them apart from organic materials such as mineral oils and aromatic heat transfer fluids. They are especially characterized by a very high thermal stability. Properly handled and maintained, HELISOL® heat transfer fluids can be operated at up to 425 °C for many years before they need replacing. Operation below these temperature maximums may provide even longer service life under most operating conditions.

HELISOL® heat transfer fluids are polydimethylsiloxanes - mixtures of linear siloxane compounds. Due to their chemical structure, they undergo rearrangement reactions (equilibration) of their silicone-oxygen bonds when operated at temperatures above 220 °C. However, this rearrangement reaction of HELISOL® heat transfer fluids is not a degradation reaction and does not affect fluid lifetime.

Because of the rearrangement reaction, some physical properties of the fluids will change throughout operation. Once the equilibrium fluid composition is reached the physical properties remain stable. The typical product data and the physical property tables are provided in the relevant technical pressure/temperature range both for the unused (HELISOL® unused) and used fluid (HELISOL® in use).

For further information about the fluid properties in the full temperature and pressure range, please refer to the HELISOL® heat transfer fluid Extended Technical Data Sheet

HELISOL® heat transfer fluids are not classified as hazardous. For more information, please consider the Material Safety Data Sheet (MSDS) of the respective product. The MSDS of all HELISOL® heat transfer fluids relate to the unused condition.

However, when HELISOL® heat transfer fluids are used as intended above 220 °C, the products of the equilibration reaction are D-cyclic siloxanes (including octamethylcyclotetrasiloxane D4 (CAS 556-67-2), decamethylcyclopentasiloxane D5 (CAS 541-02-6) and dodecamethyl-cyclohexasiloxane D6 (540-97-6).

These low-volatile components have different toxicological and flammability ratings from the unused fluid. Therefore, personnel must take appropriate handling precautions. HELISOL® in use contains substances ≥ 0.1% that have been subjected to the SVHC process according to REACH Regulation (EC) No. 1907/2006 Art. 57 as fulfilling the PBT and/or vPvB criteria according to REACH Regulation (EC) No. 1907/2006 Annex XIII.

This must be considered whenever you handle HELISOL® heat transfer fluids (as regards sampling, leaks, filling, emptying). For further information regarding the hazard identification and classification of HELISOL® heat transfer fluids “In Use,” please contact your WACKER representative.

Fluid service life in general varies with the quality of the fluid and the type and quality of the heat transfer system equipment and can vary from system to system. Significant overheating and fluid contamination will also affect the performance of a heat transfer fluid system. Properly handled and maintained, HELISOL® heat transfer fluids can be operated at 425 °C for many years before they need replacing. Operation below this temperature maximum may provide even longer service life under most operating conditions.

According to DIN 4754, HELISOL® heat transfer fluids must be checked as regards their serviceability limit state once a year or on demand. Therefore, WACKER recommends regular sampling and inspection of your heat transfer fluids.

Possible cases of demand include:

  • After the initial start-up
  • Three months after the initial start-up period
  • Irregularities of the process which could harm the heat transfer fluid, e.g. impurities, water contamination, overheating
  • Three months after changing over from a different heat transfer fluid

The most common reasons for suggesting fluid replacement are:

  • The test results of viscosity are outside the limits of action, resulting for example in impaired low-temperature fluid performance (pumpability)
  • Contamination of the heat transfer fluid with extensive quantities of water or other foreign substances (insoluble solids)

Contact your WACKER representative for details on assistance in the proper disposal of any used fluid. Please also refer to the HELISOL® heat transfer fluid Sampling Guide, which summarizes all relevant information regarding proper sampling techniques and cases of demand.

This has to be evaluated in detail because a variety of different heat transfer fluid technologies are available. Compatibility will depend on the exact chemical composition. Always consult your supplier’s technical service department for recommendations. In general, petroleum-based, aromatic chemical or synthetic fluids may not be compatible with HELISOL® heat transfer fluids at high temperatures. Deposits from oxidized, thermally degraded or contaminated organic fluids can foul interior surfaces. These fouling products are not soluble in HELISOL® heat transfer fluids, making it necessary to clean the system prior to charging with the new fluid.

At high temperatures, HELISOL® heat transfer fluids may be sensitive to various forms of contamination. Therefore, it will be necessary to ensure the exclusion of water, oxygen, oxidizing agents, alcohols, acids and bases or any contamination at operating temperature. Acids, bases or alcohols may accelerate the formation of volatile by-products, while water or oxygen/oxidizing agents can result in crosslinking of siloxane molecules and may cause a faster increase in viscosity.

To minimize these adverse effects, HELISOL® heat transfer fluids must be operated under inert conditions in technical, tightly sealed systems. For example, an inert gas blanket (e.g. nitrogen gas) on the expansion tank is required to prevent the fluid from coming into contact with the outer atmosphere. Especially when the system is being (re)filled, care should therefore be taken to prevent oxygen and moisture from entering the system with the cold fluid.

Talk to our expert for heat transfer fluids

Choosing the right heat transfer medium involves many factors. Our specialist for heat transfer media, Christian Enthammer, Marketing Manager Energy and Industrial, will be happy to discuss your specific requirements and help you find the optimal solution.

Feel free to contact him directly:

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