UltraCarb is a natural halogen-free mineral that can be used as a fire retardant filler suitable for plastics and rubbers. It is produced from a deposit of Hydromagnesite and Huntite.

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Melissa Bartz

Inside sales / Sales coordination Americas

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Each of the two minerals – Hydromagnesite and Huntite (HMH) – are flame retardants on their own. The combination gives a unique product in which we optimised specific properties. We did so by selected mining and processing to fit a variety of applications.

UltraCarb has a unique 3-stage fire retardant mechanism. Whereas the classical endothermic flame retardant fillers act by releasing water in a single action process, UltraCarb works as following:

  • Water is released at temperatures of ~220°C (thermal decomposition)
  • CO2 release at temperatures of ~330°C
  • At temperatures of ~560°C, UltraCarb particles accumulate at the surface of the burning polymer to form a stable cementitious char. This char inhibits the combustion process and thus the propagation of the fire through burning droplets.

The platy, high surface area particles of UltraCarb provide excellent properties when you use these as a functional filler in polymers. The products’ high heat absorption protects polymers from rapid thermal degradation and the formation of combustible products.

In a wide range of polymers such as polyethene (PE), polypropylene (PP), polyvinyl chloride (PVC) and rubber our customers use UltraCarb as a fire retardant filler.

UltraCarb pile in landscape

UltraCarb packaging

Our UltraCarb product range is available in paper sacks, big bags or in bulk.

UltraCarb standard grades

Primary Hydromagnesite

LH 15
(stearate surface treated) LH15C
(proprietary surface treated) LH15X

Primary Huntite

(stearate surface treated) 1251
(proprietary surface treated) 1253
(stearate surface treated) 1291
(proprietary surface treated) 1293

Stearate surface treatment:

  • improves wetting
  • and reduces the agglomeration in the compound.

Proprietary surface treatments are beneficial as an external lubricant. These act as a processing aid for extrusion and improve the LOI in EVA.

The typical properties of UltraCarb are:

Physical properties of UltraCarb:

Specific gravity [g/cm³]
Refractive index
Hardness (Mohs)
Surface area [m2/g]
11 - 17
Loose bulk density [kg/l]

Chemical properties of ATH

MgO [%]
36 - 39
CaO [%]
6 - 9
SiO2 [%]
0.2 - 1
Loss on ignition at 1,000°C
51 - 54

Hydromagnesite Huntite origin

Hydromagnesite and Huntite mineral deposits are formed by near-surface thermo-chemical geological processes. The formation of our Turkish deposits is the result of three specific conditions:

  • a depositional area of magnesium-rich ultramafic basement rocks;
  • a lake environment which evolved into a basin;
  • tectonic activity: This allowed magnesium-rich hydrothermal solutions to reach the surface.

The precipitation of Hydromagnesite and Huntite is related to the mixing of these hydrothermal solutions with fresh water from the lake environment.

Hydromagnesite Huntite toxicology

A non-toxic, non-hazardous stable mineral. You can download the Safety Data Sheet in the section on the right hand side for further information.

Downloads on request

Common questions and answers about UltraCarb

  • What is UltraCarb?


    UltraCarb products are made from rock deposits rich in hydromagnesite and huntite. Hydromagnesite has the formula Mg5(CO3)4(OH)2.4H2O and can be described as a hydrated magnesium carbonate. Huntite has the formula Mg3Ca(CO3)4 and can be described as a magnesium calcium carbonate.

  • What is HMH?


    HMH is an acronym for hydromagnesite huntite.

  • Where does UltraCarb come from?


    LKAB Minerals´ deposits of hydromagnesite and huntite are situated in the south-western region of Turkey near the city of Denizli. Processing plants are located near the ports of Izmir in Turkey and Hull in the United Kingdom.

  • In which countries do you sell UltraCarb?


    UltraCarb is available globally and sold through our local offices, please visit the product page on our website to get your nearest contact.

  • Is UltraCarb environmentally friendly?


    Advanced natural fire retardant mineral fillers are environmentally preferable to chemically produced alternatives. LKAB Minerals commissioned an evaluation of the environmental impact of UltraCarb in conformance with the ISO 14040–14044 method and found that when compared to chemically produced flame retardant fillers, such as aluminium hydroxide, greenhouse emissions, and energy consumption is 40% to 45% lower.

  • What is the shelf life of UltraCarb?


    If UltraCarb is stored in dry conditions there is no measurable change in the product.

  • If UltraCarb is stored in dry conditions there is no measurable change in the product.


    There are currently four basic UltraCarb products available. In addition, these grades are also available with two different types of surface treatment. Please contact your nearest sales manager through the UltraCarb product page.

  • What is the difference between the different types of UltraCarb?


    UltraCarb products are differentiated by 3 physical characteristics:

    • Mineral composition
    • Particle size
    • Surface modification

    The amount of hydromagnesite and huntite is fixed at two different levels for the UltraCarb “LH” and UltraCarb “1200” series respectively. The “LH” series contains more than 60% hydromagnesite whereas in the “1200” series huntite is the main mineral fraction. The actual amount of hydromagnesite and huntite in each product series is defined in internal production specifications.

  • How do you control UltraCarb composition as a natural mineral?


    LKAB Minerals has a deep and detailed understanding of its hydromagnesite and huntite mineral deposits. This means the mineral composition of the raw material feeds used for UltraCarb can be precisely controlled as part of the manufacturing process.

  • What is UltraCarb used for?


    UltraCarb is a halogen-free flame retardant filler for polymers and rubbers.

  • Is UltraCarb only used as a flame retardant filler?


    UltraCarb is also used to promote char formation. UltraCarb particles accumulate at the retreating molten polymer surface to form a stable cementitious char. This char further inhibits the combustion process and propagation of the fire from burning droplets.

  • Does UltraCarb contain halogens?


    No. UltraCarb is a halogen-free flame retardant filler.

  • What is the decomposition or reaction temperature of UltraCarb?


    UltraCarb starts to release water at 220°C. The decomposition process continues to a temperature of 550°C with a total loss in mass of 52%. The process is endothermic and absorbs approximately 1000 J per gram.

  • Do you supply compounds with UltraCarb?


    No. LKAB Minerals is the supplier of UltraCarb to many compounding companies that have built a lot of expertise.

  • Why are surface treatments offered for UltraCarb products?


    Surface treatments modify the interactions between the individual UltraCarb particles and between UltraCarb and the polymer matrix it is mixed into. This can lead to improvements in dispersion quality and fire retardancy.