Disposable hand warmers turn up the heat by means of exothermic reaction that creates rust. Each pouch typically contains iron powder (Fe), salt (NaCl), dihydrogen monoxide (H2O), activated carbon (C), and absorbent material. When the pouch is removed from its outer packaging, dioxygen (O2) drifts across the pouch's permeable covering. With NaCl and H2O present, the O2 reacts with Fe located inside to form iron oxide (Fe2O3), releasing heat.
Contents of 2 used-up disposable hand warmers are put into a dinner plate side by side. Contrast in powder's colours between 2 brands is noticeable at the interface due to oxidation level.
Contents of 2 used-up disposable hand warmers are soaked in dihydrogen monoxide (H2O). Presence of ferromagnetic material iron (Fe) in the powder was confirmed by stacked rare-earth magnet.
In Contrast, EZ Heat Instant-Reusable Hand Warmer uses phase-change crystals. Clear supersaturated solution inside the hand warmer is sodium acetate (CH3COONa) which changes phase from liquid state to solid state by heterogeneous nucleation. Unlike disposable air-activated hand warmers, EZ Heat can be recharged and used again and again.
