Why is glass wool used for the expire meant to test the action of steam on metal

Glass wool is used to generate a flow of steam.A lump of glass wool soaked in water is placed at the bottom of the boiling tube. The water present in glass wool forms steam on heating but glass wool does not take part in the reaction itself.The metal sample is placed in the middle of the horizontally kept boiling tube.The metal sample and the glass wool are heated using separate burners . The water present in glass wool form steam on heating . This steam then passes over the hot metal. The hot metal react with steam to form, the corresponding metal oxide and hydrogen gas.
Examples :
3 Fe(s) + 4 H₂O (g)$\to$ Fe₂O₃ (s)+ FeO (s)+ 4H₂ (g)

Zn(s) + H₂O (g) $\to$ZnO (s) + H₂(g)