Elastomers can tolerate ATH or MDH loadings of 60% or somewhat higher without loss of useful properties although hardness is obviously increased. ATH is substantially less costly but limits processing temperatures to below about 200–220 °C. A combination of roughly equal amounts of ATH and MDH will often be found more effective in flame retardancy than either alone. This apparent “synergism” may simply be the result of the endothermic water release occurring over a wider temperature range. Many varieties of both ATH and MDH are available, and have been characterized in our earlier polyolefins discussion. Particle size has some effect – smaller is somewhat better in some fire tests, but smaller particles also increase viscosity more. Dispersion is important, and can be made better by use of surface treated (stearic acid or silane) ATH or MDH. Silane treatments can also improve tensile, abrasion, electrical resistance and water-swell resistance. ATH or MDH are usually used at levels up to 180 phr, often with zinc borate at about 10 phr.