MDH vs ATH is the first choice to make in most halogen-free, mineral-filled compounds. Magnesium hydroxide (MDH) and aluminium trihydrate (ATH) work the same way: heated by a fire, they break down, absorb heat and release water vapour that cools and dilutes the flame. The difference is the temperature at which that happens, and it decides which polymers each one can go into. As a formulation development partner, SYCHEM TECH supplies synthetic MDH and helps compounders choose.
Short answer: choose ATH for low-temperature polymers such as EVA, LDPE, PVC, rubber and thermoset resins when cost matters most. Choose MDH when the compound is processed above about 200 °C (PP, PA, PBT), when smoke suppression is critical, or when you want a wider processing window in EVA and PE cable compounds.
How MDH and ATH stop a fire
Both are metal hydroxides. ATH breaks down from about 200–220 °C: 2 Al(OH)₃ → Al₂O₃ + 3 H₂O. MDH holds until about 340 °C: Mg(OH)₂ → MgO + H₂O. In both cases the reaction absorbs heat from the burning polymer, the water vapour dilutes the flammable gases, and the oxide left behind forms a protective layer that also traps soot.
Because they act physically rather than chemically, both are halogen-free, release no corrosive or toxic acid gases, and lower smoke density. The price is loading: a compound needs around 50–65% of either filler to reach typical cable or UL94 targets, which is why surface treatment and dispersion matter so much.
MDH vs ATH comparison table
| Property | MDH (magnesium hydroxide) | ATH (aluminium trihydrate) |
|---|---|---|
| Formula | Mg(OH)₂ | Al(OH)₃ |
| Water release begins | About 340 °C | About 200–220 °C |
| Heat absorbed on decomposition | About 1,300 kJ/kg | About 1,100 kJ/kg |
| Residue | MgO | Al₂O₃ |
| Smoke suppression | Excellent | Good |
| Suitable polymers | EVA, PE, PP, PA, PBT, rubber; also low-temperature polymers | EVA, LDPE, PVC, rubber, thermoset resins; low-temperature processing only |
| Typical loading for V-0 or cable specs | About 50–65% in polyolefins; 35–45% in PA | Similar high loadings, about 50–65% |
| Density | About 2.36 g/cm³ | About 2.4 g/cm³ |
| Mohs hardness | About 2.5 (less abrasive) | About 3 |
| pH | Mildly alkaline, about 10 | Close to neutral; amphoteric |
| Price | Higher | Lower; the largest-volume flame retardant |
MDH values are from our magnesium hydroxide product page; ATH values are typical published figures. Grades differ in particle size and coating, so ask for the TDS of the exact grade.
MDH vs ATH by polymer: processing temperature decides
If the melt temperature in the extruder or molding machine reaches the point where the filler starts to lose water, the compound foams, the surface turns rough and the flame retardant is used up before the part is even made. Match the filler to the polymer’s processing window:
| Polymer | Typical melt temperature | ATH | MDH |
|---|---|---|---|
| EVA, LDPE cable compounds | About 160–200 °C | Yes | Yes |
| PVC, rubber, thermoset resins | Low, or cured below 200 °C | Yes | Yes |
| PP | About 200–240 °C | Marginal; only with careful low-temperature processing | Yes |
| PA6, PBT | About 240–270 °C | No | Yes |
| PA66 | About 270–300 °C | No | Yes |
When ATH is the better choice
- EVA and LDPE cable compounds processed below about 200 °C, where ATH gives the lowest cost
- PVC, rubber and latex compounds and foams
- Thermoset resins such as unsaturated polyester, epoxy and SMC/BMC, which cure at low temperature
- White or light-coloured products where ATH’s whiteness and price suit the formula
- Existing approved formulas built and certified around ATH
When MDH is the better choice
- PP compounds, which melt above the temperature where ATH starts to break down; see our PP resin range
- Engineering plastics such as PA6, PA66 and PBT, processed at 240–300 °C; see PA6 vs PA66
- LSZH cable for transit, marine and buildings, where smoke density limits are strict
- EV battery components such as pack covers and busbar insulation
- High-speed cable extrusion, where a wider temperature margin keeps the line stable
- Rubber compounds that need a hotter cure or better smoke performance
Formulation tips for MDH and ATH compounds
- Use coated grades. Fatty-acid or silane surface treatment helps the filler wet out and keeps elongation and melt flow acceptable at high loadings. Our MDH is fatty-acid coated, and 0.5–1.5% silane improves mechanical retention further.
- Fine, narrow particle size. A D50 below about 2 µm gives better flame performance and mechanical properties than coarse grades.
- Add a coupling polymer. In EVA and PE cable compounds, a maleic-anhydride-grafted PE such as our SY-PX or SY-PZ compatibilizers bonds the polymer to the filler and helps elongation and tensile strength.
- Choose a carrier that takes the filler. EVA and soft POE accept 55–65% filler and keep their flexibility.
- Blending is allowed. ATH and MDH are often combined in cable compounds to balance cost and processing margin; the blend must still stay below the ATH limit during processing.
- Combine with phosphorus. A phosphorus-nitrogen system can lower the total mineral loading; our phosphorus vs MDH comparison explains how the two mechanisms work together, and our HF-80 and HF-90 systems are used at an MDH:phosphorus ratio of about 3:1 to 5:1.
- Dry the filler. Moisture in the filler causes porosity in the extrudate; keep bags sealed and dry before use.
MDH vs ATH cost: compare the compound, not the filler
ATH is cheaper per kilogram and is the largest-volume flame retardant in the world, so for EVA and LDPE compounds processed at low temperature it is usually the economical choice. MDH costs more but opens up PP and engineering plastics, tolerates hotter and faster processing, and suppresses smoke better. At loadings of 50–65%, the filler price drives the compound price, so compare the cost of a compound that actually passes your flame and smoke test, at your line speed.
Frequently asked questions
Is MDH better than ATH?
Not always. MDH is the better technical choice above about 200 °C and where smoke suppression is critical. ATH is the more economical choice for low-temperature polymers such as EVA, LDPE, PVC and thermosets.
Can ATH be used in polypropylene?
Only with difficulty. PP is normally processed above the temperature where ATH starts to release water, so the compound can foam. MDH is the standard mineral flame retardant for PP.
Can I mix ATH and MDH?
Yes. Blends are common in cable compounds to balance cost and processing margin. Keep the processing temperature below the point where ATH starts to break down.
How much MDH is needed for UL94 V-0?
As a starting point, about 50–60% in PP or PE at 1.5 mm, 55–65% in EVA cable compounds and 35–45% in PA6 or PA66 at 1.6 mm. Adding a phosphorus system can lower the total loading.
Do you supply ATH?
We focus on synthetic MDH and phosphorus-based flame retardants. If your compound is a low-temperature EVA or PE cable formula where ATH is the right answer, tell us and we will advise on the formula.
Get an MDH recommendation
Still weighing MDH vs ATH? Tell us the polymer, processing temperature, target rating (UL94 or cable standard) and smoke requirement. We will suggest an MDH grade and loading, check whether a phosphorus system can lower it, email you the TDS and arrange samples. Contact our technical team or write to info@sychemtech.com.
Related products: our magnesium hydroxide flame retardant, phosphorus-based flame retardants and the full flame retardant range, SY series compatibilizers for halogen-free cable, and antioxidants for heat ageing.
