UltraCarb is a halogen-free fire retardant filler for polymers and rubbers produced from naturally occurring mixtures containing two minerals: hydromagnesite and huntite.

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Paul Pasquino

Paul Pasquino

President / Managing Director Americas

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Nature’s own fire retardant

This unique natural mixture of minerals is also known as HMH and is a proven fire retardant filler in a wide range of polymers and rubbers such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), ethylene-propylene diene monomer (EPDM) and nitrile rubber (NBR).

The combination gives a unique product in which specific properties can be optimized by selected mining and processing to fit a variety of applications.

Unique fire retardant properties

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, our premium product works as follows:

  • Water is released at temperatures of ~220°C (thermal decomposition)
  • CO2 release at temperatures of ~330°C
  • At temperatures of ~560°C, 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 our halogen-free mineral 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.

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
Primary Huntite
(stearate surface treated) 1251
(stearate surface treated) LH15C
(proprietary surface treated) 1253
(proprietary surface treated) LH15X
(proprietary surface treated) 1291

Stearate surface treatment improves wetting and reduces the agglomeration in the compound, proprietary surface treatments are beneficial as an external lubricant, 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 UltraCarb

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

UltraCarb origin

The naturally occurring mixtures  of Hydromagnesite and Huntite mineral deposits are formed by near surface thermo-chemical geological processes. The formation of our Turkish desposits 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 HMH  is related to the mixing of these hydrothermal solutions with fresh water from the lake environment.

HMH toxicology

Our UltraCarb is a non-toxic, non-hazardous stable mineral. You can download the Safety Data Sheet in the documentation section for further information.

For your convenience, we have created several videos related to UltraCarb and its applications, which you can watch in your own time.


  • UltraCarb – Life Cycle Analysis – 00m49s – A detailed and independently controlled Life Cycle Assessment of UltraCarb showed how significantly more environmental friendly UltraCarb is. We took a full life cycle comparing it to traditional aluminium hydroxide (ATH) flame retardants.

Webinars and courses

We have not recorded yet any webinar on UltraCarb. But please check our Learning Centre to see an overview of all courses and webinar we do offer in relation to our portfolio. There might be some to your liking.

Common questions and answers about UltraCarb

  • What is UltraCarb?


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

  • What is HMH?


    HMH is an acronym for hydromagnesite huntite.

  • 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.

  • Where does UltraCarb come from?


    LKAB Minerals´ deposits 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.

  • 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 the 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.

  • How many different types of UltraCarb do you offer?


    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:
    1) Mineral composition
    2) Particle size
    3) Surface modification
    The amount of the naturally occurring mixtures 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 the naturally occurring 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 naturally occurring mixtures of minerals 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.

Product Definition