Stone wool is mainly made from natural rocks while slag wool is from blast furnace cinder, phosphate slag, fly ash etc.
Iron ions inside the basalt allow finished stone wool products to have a higher content of iron oxide, enhancing its resistance to fire and high temperature. The content of slag or cinder is neither known nor evenly distributed, their pellet size irregular which causes the fact that some do not melt due to uneven heating. Furnace cinder may contain harmful heavy metals that are unknown. Acidic oxides containing sulfur, phosphorus and other elements will turn into acid with water, developing to metal corrosion; the exposure to water plus a high content of chloride ion will also generate acid that corrodes metals.
Melting basalt requires a temperature of more than 1,500 ° C, while slag and furnace cinder melt at 800 to 1,000 ° C. They start to shrink and deform at above 800 ° C, and even can be witnessed with holes, crystallization and carbonation. The burning test proved that slag wool performs poorly in fire resistance.
Slag wool has very coarse fiber and a high content of slag ball, which results in high thermal conductivity and poor performance in insulation. It often causes skin irritation and allergies. Raw materials being industrial waste or blast furnace cinder, slag cotton contains lots of powder and dust that carry heavy metal ions and sulfide. The contact with skin or inhalation will cause long-term harm on people.