Steel wool, which is a bundle of randomly arranged thin wires, can be set on fire. It is common to think that substances lose mass during burning, but the mass of burned steel wool, on the contrary, increases. This happens due to the attachment of oxygen atoms to the material, turning part of the iron into iron oxide.
This process is a result of a chemical reaction where iron in the steel wool reacts with oxygen in the air. When steel wool burns, it combines with oxygen to form iron oxide (rust), adding the mass of the oxygen to the original mass of the steel wool.
This is why, after the combustion, the remaining steel wool weighs more than it did before being burned. This phenomenon illustrates the principle of mass conservation in chemical reactions, where the total mass of reactants equals the total mass of products.