UltraCarb is a halogen free fire retardant produced from our own natural deposits containing two minerals: hydromagnesite and huntite.
This unique mineral combination is known as HMH.



UltraCarb has a unique 3-stage fire retardant mechanism. It is used in a wide range of polymers such as polyethylene, polypropylene and PVC.


Thermal decomposition of UltraCarb begins at 220°C. The two mechanisms are endothermic and absorb approximately 1000 J/g. The high heat absorption of UltraCarb protects polymers from a rapid thermal degradation and the formation of combustible products.

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 through burning particles.

3 Stage fire retardant mechanism

Standard grades Application development

To provide our customers with the best possible service and fitting solutions, our R&D and Technical Departments are able to offer joint product development.

Quality & environment

Advanced natural fire retardant mineral fillers are environmentally preferable to chemically produced alternatives. In recognition of this, LKAB Minerals has developed special in-house beneficiation and processing techniques and focuses on producing highly consistent and well defined products.
The LKAB Group is committed to being one of the most innovative, resource and climate efficient mining companies in the world. Therefore, the company commissioned an evaluation of the environmental impact of UltraCarb in conformance with the ISO 14040-14044 method and found that when compared to traditional flame retardant fillers, such as aluminium hydroxide, greenhouse emissions, and energy consumption is 40% – 45% lower.


  • Physical properties Typical values:
    Specific gravity:2.4 g/cm3
    Refractive index:1.56
    Surface area:11 – 17 m2/g
    Hardness (Mohs’):2.5
    Loose bulk density:0.4 kg/ltr
  • Chemical composition Typical values (%):
    Magnesium as MgO:36 – 39
    Calcium as CaO:6 – 9
    Silica as SiO2:0,2 – 1
    Loss on ignition at 1000°C:51 – 54

Standard grades

All our UltraCarb products are offered with surface treatment.
Stearic acid treated grades are:
LH3C, LH15C, 1251, 1291
Poly di-methyl siloxane (PDMS) treated grades are:
LH3X, LH15X, 1253, 1293